EXHIBIT 99.2 Long Duration Energy Storage Systems Energy Storage for for a Cleaner Future a Cleaner Future CONFIDENTIAL APRIL 2021EXHIBIT 99.2 Long Duration Energy Storage Systems Energy Storage for for a Cleaner Future a Cleaner Future CONFIDENTIAL APRIL 2021

Disclaimers This presentation (this “Presentation”) was prepared for informational purposes only to assist interested parties in making their own evaluation of the proposed transaction (the “Transaction”) between Acon S2 Acquisition Corp. (“ACON”, “we”, or “our”) and ESS Inc. (“ESS”). This Presentation is for discussion purposes only and does not constitute an offer to purchase nor a solicitation of an offer to sell shares of ACON, ESS or any successor entity of the Transaction, nor shall there be any sale of securities in any jurisdiction in which such offer, solicitation, or sale would be unlawful prior to registration or qualification under the securities laws of any such jurisdiction. This Presentation is not intended to form the basis of any investment decision by the recipient and does not constitute investment, tax or legal advice. No representation, express or implied, is or will be given by ACON, ESS or their respective affiliates and advisors as to the accuracy or completeness of the information contained herein, or any other written or oral information made available in the course of an evaluation of the Transaction. This Presentation provided by ACON and ESS may contain certain forward looking statements, including statements regarding ACON’s, ESS’s or their management teams’ expectations, hopes, beliefs, intentions or strategies regarding the future. The words “anticipate”, “believe”, “continue”, “could”, “estimate”, “expect”, “intends”, “may”, “might”, “plan”, “possible”, “potential”, “predict”, “project”, “should”, “would” and similar expressions may identify forward-looking statements, but the absence of these words does not mean that a statement is not forward-looking. These forward-looking statements are based on ACON’s and ESS’s current expectations and beliefs concerning future developments and their potential effects on ACON, ESS or any successor entity of the Transaction. Many factors could cause actual future events to differ materially from the forward-looking statements in this presentation, including but not limited to: (i) the risk that the Transaction may not be completed in a timely manner or at all, which may adversely affect the price of ACON’s securities, (ii) the failure to satisfy the conditions to the consummation of the Transaction, (iii) the occurrence of any event, change or other circumstance that could give rise to the termination of the Agreement and Plan of Merger, (iv) the effect of the announcement or pendency of the Transaction on ESS’s business relationships, operating results and business generally, (v) risks that the Transaction disrupts current plans and operations of ESS, (vi) changes in the competitive and highly regulated industries in which ESS plans to operate, variations in operating performance across competitors, changes in laws and regulations affecting ESS’s business and changes in the combined capital structure, (vii) the ability to implement business plans, forecasts and other expectations after the completion of the Transaction, and identify and realize additional opportunities, and (viii) such other risks and uncertainties included in the separate summary risk factors. There can be no assurance that the future developments affecting ACON, ESS or any successor entity of the Transaction will be those that we have anticipated. These forward-looking statements involve a number of risks, uncertainties (some of which are beyond ACON’s or ESS’s control) or other assumptions that may cause actual results or performance to be materially different from those expressed or implied by these forward-looking statements. Except as required by law, ACON and ESS are not undertaking any obligation to update or revise any forward-looking statements whether as a result of new information, future events or otherwise. All rights to the trademarks, copyrights, logos and other intellectual property listed herein belong to their respective owners and ACON’s or ESS’s use thereof does not imply an affiliation with, or endorsement by the owners of such trademarks, copyrights, logos and other intellectual property. Solely for convenience, trademarks and trade names referred to in this Presentation may appear with the ® or ™ symbols, but such references are not intended to indicate, in any way, that such names and logos are trademarks or registered trademarks of ACON. Use of Projections. The financial and operating forecasts and projections contained herein represent certain estimates of ESS as of the date thereof. Neither ACON’s nor ESS’s independent public accountants have examined, reviewed or compiled the forecasts or projections and, accordingly, neither expresses an opinion or other form of assurance with respect thereto. Furthermore none of ACON, ESS nor their respective management teams can give any assurance that the forecasts or projections contained herein accurately represents ESS’s future operations or financial conditions. Such information is subject to a wide variety of significant business, economic and competitive risks and uncertainties, including but not limited to those set forth in the second paragraph above that could cause actual results to differ materially from those contained in the prospective financial information. Accordingly, there can be no assurance that the prospective results are indicative of the future performance of ACON or ESS or that actual results will not differ materially from those presented in the prospective financial information. Some of the assumptions upon which the projections are based inevitably will not materialize and unanticipated events may occur that could affect results. Therefore, actual results achieved during the periods covered by the projections may vary and may vary materially from the projected results. Inclusion of the prospective financial information in this presentation should not be regarded as a representation by any person that the results contained in the prospective financial information are indicative of future results or will be achieved. This Presentation contains statistical data, estimates and forecasts that are based on independent industry publications or other publicly available information. This information involves many assumptions and limitations and you are cautioned not to give undue weight to these estimates. We have not independently verified the accuracy or completeness of the data that has been contained in these industry publications and other publicly available information. Accordingly, none of ACON, ESS nor their respective affiliates and advisors makes any representations as to the accuracy or completeness of these data. This Presentation contains references to ESS’s achievements compared to other companies. All of such references are based on the belief of ESS’s management based on publicly available information known to ESS’s management. Non-GAAP Financial Measures. The financial information and data contained in this Presentation is unaudited and does not conform to Regulation S-X promulgated under the Securities Act of 1933, as amended. This Presentation also includes non-GAAP financial measures, including gross margin and Adjusted EBITDA. ACON and ESS believe that these non-GAAP measures of financial results provide useful information to management and investors regarding certain financial and business trends relating to ESS’s financial condition and results of operations. ESS’s management uses certain of these non-GAAP measures to compare ESS’s performance to that of prior periods for trend analyses and for budgeting and planning purposes. Not all of the information necessary for a quantitative reconciliation of these forward-looking non-GAAP financial measures to the most directly comparable GAAP financial measures is available without unreasonable efforts at this time. Specifically, ESS does not provide such quantitative reconciliation due to the inherent difficulty in forecasting and quantifying certain amounts that are necessary for such reconciliations. This Presentation relates to a proposed transaction between ESS and ACON. This Presentation does not constitute an offer to sell or exchange, or the solicitation of an offer to buy or exchange, any securities, nor shall there be any sale of securities in any jurisdiction in which such offer, sale or exchange would be unlawful prior to registration or qualification under the securities laws of any such jurisdiction. ACON and ESS intend to file a registration statement on Form S-4 with the U.S. Securities and Exchange Commission (the “SEC”), which will include a document that serves as a joint prospectus and proxy statement, referred to as a proxy statement/prospectus. A proxy statement/prospectus will be sent to all ESS and ACON shareholders. ESS and ACON will also file other documents regarding the proposed transaction with the SEC. Before making any voting decision, investors and security holders of ESS and ACON are urged to read the registration statement, the proxy statement/prospectus and all other relevant documents filed or that will be filed with the SEC in connection with the proposed transaction as they become available because they will contain important information about the proposed transaction. Investors and security holders will be able to obtain free copies of the registration statement, the proxy statement/prospectus and all other relevant documents filed or that will be filed with the SEC by ESS and ACON through the website maintained by the SEC at www.sec.gov. Participants in the Solicitation. ESS, ACON and their respective directors and executive officers may be deemed to be participants in the solicitation of proxies from ACON’s shareholders in connection with the proposed transaction. A list of the names of such directors, executive officers, other members of management, and employees, and information regarding their interests in the business combination will be contained in ACON’s filings with the SEC, and such information and names of ESS’s directors and executive officers will also be in the Registration Statement on Form S-4 to be filed with the SEC by ACON, which will include the proxy statement of ACON. Additional information regarding the interests of such potential participants in the solicitation process will also be included in the registration statement (and will be included in the definitive proxy statement/prospectus) and other relevant documents when they are filed with the SEC. CONFIDENTIAL CON CONF FIID DEN ENT TIIA AL L 1Disclaimers This presentation (this “Presentation”) was prepared for informational purposes only to assist interested parties in making their own evaluation of the proposed transaction (the “Transaction”) between Acon S2 Acquisition Corp. (“ACON”, “we”, or “our”) and ESS Inc. (“ESS”). This Presentation is for discussion purposes only and does not constitute an offer to purchase nor a solicitation of an offer to sell shares of ACON, ESS or any successor entity of the Transaction, nor shall there be any sale of securities in any jurisdiction in which such offer, solicitation, or sale would be unlawful prior to registration or qualification under the securities laws of any such jurisdiction. This Presentation is not intended to form the basis of any investment decision by the recipient and does not constitute investment, tax or legal advice. No representation, express or implied, is or will be given by ACON, ESS or their respective affiliates and advisors as to the accuracy or completeness of the information contained herein, or any other written or oral information made available in the course of an evaluation of the Transaction. This Presentation provided by ACON and ESS may contain certain forward looking statements, including statements regarding ACON’s, ESS’s or their management teams’ expectations, hopes, beliefs, intentions or strategies regarding the future. The words “anticipate”, “believe”, “continue”, “could”, “estimate”, “expect”, “intends”, “may”, “might”, “plan”, “possible”, “potential”, “predict”, “project”, “should”, “would” and similar expressions may identify forward-looking statements, but the absence of these words does not mean that a statement is not forward-looking. These forward-looking statements are based on ACON’s and ESS’s current expectations and beliefs concerning future developments and their potential effects on ACON, ESS or any successor entity of the Transaction. Many factors could cause actual future events to differ materially from the forward-looking statements in this presentation, including but not limited to: (i) the risk that the Transaction may not be completed in a timely manner or at all, which may adversely affect the price of ACON’s securities, (ii) the failure to satisfy the conditions to the consummation of the Transaction, (iii) the occurrence of any event, change or other circumstance that could give rise to the termination of the Agreement and Plan of Merger, (iv) the effect of the announcement or pendency of the Transaction on ESS’s business relationships, operating results and business generally, (v) risks that the Transaction disrupts current plans and operations of ESS, (vi) changes in the competitive and highly regulated industries in which ESS plans to operate, variations in operating performance across competitors, changes in laws and regulations affecting ESS’s business and changes in the combined capital structure, (vii) the ability to implement business plans, forecasts and other expectations after the completion of the Transaction, and identify and realize additional opportunities, and (viii) such other risks and uncertainties included in the separate summary risk factors. There can be no assurance that the future developments affecting ACON, ESS or any successor entity of the Transaction will be those that we have anticipated. These forward-looking statements involve a number of risks, uncertainties (some of which are beyond ACON’s or ESS’s control) or other assumptions that may cause actual results or performance to be materially different from those expressed or implied by these forward-looking statements. Except as required by law, ACON and ESS are not undertaking any obligation to update or revise any forward-looking statements whether as a result of new information, future events or otherwise. All rights to the trademarks, copyrights, logos and other intellectual property listed herein belong to their respective owners and ACON’s or ESS’s use thereof does not imply an affiliation with, or endorsement by the owners of such trademarks, copyrights, logos and other intellectual property. Solely for convenience, trademarks and trade names referred to in this Presentation may appear with the ® or ™ symbols, but such references are not intended to indicate, in any way, that such names and logos are trademarks or registered trademarks of ACON. Use of Projections. The financial and operating forecasts and projections contained herein represent certain estimates of ESS as of the date thereof. Neither ACON’s nor ESS’s independent public accountants have examined, reviewed or compiled the forecasts or projections and, accordingly, neither expresses an opinion or other form of assurance with respect thereto. Furthermore none of ACON, ESS nor their respective management teams can give any assurance that the forecasts or projections contained herein accurately represents ESS’s future operations or financial conditions. Such information is subject to a wide variety of significant business, economic and competitive risks and uncertainties, including but not limited to those set forth in the second paragraph above that could cause actual results to differ materially from those contained in the prospective financial information. Accordingly, there can be no assurance that the prospective results are indicative of the future performance of ACON or ESS or that actual results will not differ materially from those presented in the prospective financial information. Some of the assumptions upon which the projections are based inevitably will not materialize and unanticipated events may occur that could affect results. Therefore, actual results achieved during the periods covered by the projections may vary and may vary materially from the projected results. Inclusion of the prospective financial information in this presentation should not be regarded as a representation by any person that the results contained in the prospective financial information are indicative of future results or will be achieved. This Presentation contains statistical data, estimates and forecasts that are based on independent industry publications or other publicly available information. This information involves many assumptions and limitations and you are cautioned not to give undue weight to these estimates. We have not independently verified the accuracy or completeness of the data that has been contained in these industry publications and other publicly available information. Accordingly, none of ACON, ESS nor their respective affiliates and advisors makes any representations as to the accuracy or completeness of these data. This Presentation contains references to ESS’s achievements compared to other companies. All of such references are based on the belief of ESS’s management based on publicly available information known to ESS’s management. Non-GAAP Financial Measures. The financial information and data contained in this Presentation is unaudited and does not conform to Regulation S-X promulgated under the Securities Act of 1933, as amended. This Presentation also includes non-GAAP financial measures, including gross margin and Adjusted EBITDA. ACON and ESS believe that these non-GAAP measures of financial results provide useful information to management and investors regarding certain financial and business trends relating to ESS’s financial condition and results of operations. ESS’s management uses certain of these non-GAAP measures to compare ESS’s performance to that of prior periods for trend analyses and for budgeting and planning purposes. Not all of the information necessary for a quantitative reconciliation of these forward-looking non-GAAP financial measures to the most directly comparable GAAP financial measures is available without unreasonable efforts at this time. Specifically, ESS does not provide such quantitative reconciliation due to the inherent difficulty in forecasting and quantifying certain amounts that are necessary for such reconciliations. This Presentation relates to a proposed transaction between ESS and ACON. This Presentation does not constitute an offer to sell or exchange, or the solicitation of an offer to buy or exchange, any securities, nor shall there be any sale of securities in any jurisdiction in which such offer, sale or exchange would be unlawful prior to registration or qualification under the securities laws of any such jurisdiction. ACON and ESS intend to file a registration statement on Form S-4 with the U.S. Securities and Exchange Commission (the “SEC”), which will include a document that serves as a joint prospectus and proxy statement, referred to as a proxy statement/prospectus. A proxy statement/prospectus will be sent to all ESS and ACON shareholders. ESS and ACON will also file other documents regarding the proposed transaction with the SEC. Before making any voting decision, investors and security holders of ESS and ACON are urged to read the registration statement, the proxy statement/prospectus and all other relevant documents filed or that will be filed with the SEC in connection with the proposed transaction as they become available because they will contain important information about the proposed transaction. Investors and security holders will be able to obtain free copies of the registration statement, the proxy statement/prospectus and all other relevant documents filed or that will be filed with the SEC by ESS and ACON through the website maintained by the SEC at www.sec.gov. Participants in the Solicitation. ESS, ACON and their respective directors and executive officers may be deemed to be participants in the solicitation of proxies from ACON’s shareholders in connection with the proposed transaction. A list of the names of such directors, executive officers, other members of management, and employees, and information regarding their interests in the business combination will be contained in ACON’s filings with the SEC, and such information and names of ESS’s directors and executive officers will also be in the Registration Statement on Form S-4 to be filed with the SEC by ACON, which will include the proxy statement of ACON. Additional information regarding the interests of such potential participants in the solicitation process will also be included in the registration statement (and will be included in the definitive proxy statement/prospectus) and other relevant documents when they are filed with the SEC. CONFIDENTIAL CON CONF FIID DEN ENT TIIA AL L 1

Game Changing Technology The Power Grid of the Future – Feasible Today STABLE. SECURE. CLEAN. CONFIDENTIAL 2 2Game Changing Technology The Power Grid of the Future – Feasible Today STABLE. SECURE. CLEAN. CONFIDENTIAL 2 2

Transaction Overview Category Catalyst in Long Duration Energy Storage Solutions Leadership § Founded in 2011 to enable the stable, decentralized ESS and decarbonized power grid of the future § ACON S2 (NASDAQ: STWO): a special purpose Offering Size acquisition company § $250 million cash in trust § PIPE size of $250 million Craig Evans Eric Dresselhuys Julia Song Amir Moftakhar § $1,072 million pro forma enterprise value Valuation President & Founder CEO CTO & Founder CFO (March 2021) § Attractive value, high-growth, genuinely sustainable business § ESS shareholders rolling 100% of equity Capital Structure § $465 million net proceeds (assuming no redemptions) § Fully funded to projected cash flow profitability ESS’ Key Investors Adam Kriger John Roush Alan Greenshields and Partners CEO & Director CFO & Chairman ACON Advisor CON CONF FIID DEN ENT TIIA AL L 3 Note For additional information, please refer to the Detailed Transaction Overview on p. 36 of this presentation.Transaction Overview Category Catalyst in Long Duration Energy Storage Solutions Leadership § Founded in 2011 to enable the stable, decentralized ESS and decarbonized power grid of the future § ACON S2 (NASDAQ: STWO): a special purpose Offering Size acquisition company § $250 million cash in trust § PIPE size of $250 million Craig Evans Eric Dresselhuys Julia Song Amir Moftakhar § $1,072 million pro forma enterprise value Valuation President & Founder CEO CTO & Founder CFO (March 2021) § Attractive value, high-growth, genuinely sustainable business § ESS shareholders rolling 100% of equity Capital Structure § $465 million net proceeds (assuming no redemptions) § Fully funded to projected cash flow profitability ESS’ Key Investors Adam Kriger John Roush Alan Greenshields and Partners CEO & Director CFO & Chairman ACON Advisor CON CONF FIID DEN ENT TIIA AL L 3 Note For additional information, please refer to the Detailed Transaction Overview on p. 36 of this presentation.

We Must Reimagine the Grid Aging Infrastructure Severe Weather Events Rising Renewables Penetration Growing Energy Demand CON CON CONF F FIIID D DEN EN ENT T TIIIA A AL L L 4 4We Must Reimagine the Grid Aging Infrastructure Severe Weather Events Rising Renewables Penetration Growing Energy Demand CON CON CONF F FIIID D DEN EN ENT T TIIIA A AL L L 4 4

Energy Transition is Building Momentum Stakeholders are aligned to accelerate the energy transition towards a more sustainable future Consumer “Anybody who has the breakthrough on battery storage is Preferences going to have the key to the future” John Kerry (U.S. Special Presidential Envoy for Climate) “It’s a question of when, not if, the global economy will shift way from fossil fuels” Corporate Regulatory Bloomberg Commitments Energy “Renewables should supply 90% of all energy needs…fossil Transition fuel usage would fall by 75%” IRENA “Transmission and energy storage certainly have critical roles to play, with broader interconnection and high voltage transmission corridors to build regional resilience” Investor Capital Mandates Markets Nuclear Innovation Alliance CON CONF FIID DEN ENT TIIA AL L 5Energy Transition is Building Momentum Stakeholders are aligned to accelerate the energy transition towards a more sustainable future Consumer “Anybody who has the breakthrough on battery storage is Preferences going to have the key to the future” John Kerry (U.S. Special Presidential Envoy for Climate) “It’s a question of when, not if, the global economy will shift way from fossil fuels” Corporate Regulatory Bloomberg Commitments Energy “Renewables should supply 90% of all energy needs…fossil Transition fuel usage would fall by 75%” IRENA “Transmission and energy storage certainly have critical roles to play, with broader interconnection and high voltage transmission corridors to build regional resilience” Investor Capital Mandates Markets Nuclear Innovation Alliance CON CONF FIID DEN ENT TIIA AL L 5

ESS is a Game Changer in Long Duration Energy Storage Enables up to 100% Allows Proliferation Stabilizes the Grid Renewable Penetration of Microgrids CON CONF FIID DEN ENT TIIA AL L 6ESS is a Game Changer in Long Duration Energy Storage Enables up to 100% Allows Proliferation Stabilizes the Grid Renewable Penetration of Microgrids CON CONF FIID DEN ENT TIIA AL L 6

ESS: A Category Defining Investment Opportunity 1 Large and Fast-Growing TAM: ~$56bn by 2027 growing at a 33% CAGR 1 Simple Yet Revolutionary Technology: Iron, salt and water; strong patent portfolio 2 2 Compelling Value Proposition: Highest performance, lowest cost and most sustainable 3 3 Low Risk Expansion Plan: Field proven technology with low-cost manufacturing build out 4 4 $7bn of Identified Opportunities : $300m+ SoftBank Energy framework agreement through 2026 5 Premier Management Team: Founders and inventors supported by an experienced team 6 1 Guidehouse Insights, ‘Market Data: Utility-Scale Energy Storage Market Update’, 3Q 2020; Guidehouse Insights, ‘Market Data: Energy Storage for Microgrids and Remote Power Systems’, 2Q 2020; and Navigant Research, ‘Distributed Energy Storage Overview’, 4Q 2019. 2 Management Estimates of levelized cost of storage (LCOS) among long duration Storage Systems. 3 Based on our Generation I products, which are no longer deployed. CON CONF FIID DEN ENT TIIA AL L 7 4 Pipeline of visible potential orders.ESS: A Category Defining Investment Opportunity 1 Large and Fast-Growing TAM: ~$56bn by 2027 growing at a 33% CAGR 1 Simple Yet Revolutionary Technology: Iron, salt and water; strong patent portfolio 2 2 Compelling Value Proposition: Highest performance, lowest cost and most sustainable 3 3 Low Risk Expansion Plan: Field proven technology with low-cost manufacturing build out 4 4 $7bn of Identified Opportunities : $300m+ SoftBank Energy framework agreement through 2026 5 Premier Management Team: Founders and inventors supported by an experienced team 6 1 Guidehouse Insights, ‘Market Data: Utility-Scale Energy Storage Market Update’, 3Q 2020; Guidehouse Insights, ‘Market Data: Energy Storage for Microgrids and Remote Power Systems’, 2Q 2020; and Navigant Research, ‘Distributed Energy Storage Overview’, 4Q 2019. 2 Management Estimates of levelized cost of storage (LCOS) among long duration Storage Systems. 3 Based on our Generation I products, which are no longer deployed. CON CONF FIID DEN ENT TIIA AL L 7 4 Pipeline of visible potential orders.

Market Opportunity CON CONF FIID DEN ENT TIIA AL L 8 8Market Opportunity CON CONF FIID DEN ENT TIIA AL L 8 8

What Is Long Duration Storage? Low Cost to Enable Shift Supply to Meet Reliable Replacement of Alternatives Demand from 4 – 12 Hours (Grid Stability) (Peaker Plants) CON CON CON CONF F F FIIIID D D DEN EN EN ENT T T TIIIIA A A AL L L L 9 9What Is Long Duration Storage? Low Cost to Enable Shift Supply to Meet Reliable Replacement of Alternatives Demand from 4 – 12 Hours (Grid Stability) (Peaker Plants) CON CON CON CONF F F FIIIID D D DEN EN EN ENT T T TIIIIA A A AL L L L 9 9

ESS Transforms the Value Proposition for Long Duration Storage What Customers Demand How ESS Transforms the Grid § Can replace coal and natural gas with solar and § Up to 12 hours wind power Longer Duration § Flexibility allows multiple revenue streams § Greater resiliency to unexpected events § Step function improvement in economics of § Lower LCOS than other technologies in the market storage Low Cost § Incremental cost of storage <$20/kWh § Enables multiple use cases § <1 second response time § Improved grid resiliency and flexibility Power On Demand § >20,000 cycle life – $0 marginal cost per cycle § Can deploy in a wide range of geographies and § Non-flammable, non-toxic, no explosion risk climates Safety and Reliability § Munich RE insures technology risk§ Customers can be confident in a long-term solution § Easily sourced materials; recyclable components§ Environmentally sustainable Sustainability § “Plug and play” with 25-year operating life§ Accelerates clean energy transition CON CONF FIID DEN ENT TIIA AL L 10ESS Transforms the Value Proposition for Long Duration Storage What Customers Demand How ESS Transforms the Grid § Can replace coal and natural gas with solar and § Up to 12 hours wind power Longer Duration § Flexibility allows multiple revenue streams § Greater resiliency to unexpected events § Step function improvement in economics of § Lower LCOS than other technologies in the market storage Low Cost § Incremental cost of storage <$20/kWh § Enables multiple use cases § <1 second response time § Improved grid resiliency and flexibility Power On Demand § >20,000 cycle life – $0 marginal cost per cycle § Can deploy in a wide range of geographies and § Non-flammable, non-toxic, no explosion risk climates Safety and Reliability § Munich RE insures technology risk§ Customers can be confident in a long-term solution § Easily sourced materials; recyclable components§ Environmentally sustainable Sustainability § “Plug and play” with 25-year operating life§ Accelerates clean energy transition CON CONF FIID DEN ENT TIIA AL L 10

Stabilize the Grid and Accelerate Renewables 1 US Renewable Energy Penetration (2015-2050) Renewable intermittency creates a 65% massive problem for the grid, 57% 47% particularly >25% penetration 40% 36% 31% 23% 15% § Carbon-free is the goal 2015 2020 2025 2030 2035 2040 2045 2050 § Intermittency and curtailment are barriers 1,2 California Duck Curve and % Renewable Penetration § 4-hour storage does not efficiently bridge 2013 (10%) 2019 (27%) 25 the duck curve Impact of 15 § Longer duration solutions enable peaker renewables on the grid plant replacements 5 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Hour of day 1 BloombergNEF. CON CONF FIID DEN ENT TIIA AL L 11 2 IEA, “The California Duck Curve”, December 2019. % figures represent solar and wind power penetration in each year. GWStabilize the Grid and Accelerate Renewables 1 US Renewable Energy Penetration (2015-2050) Renewable intermittency creates a 65% massive problem for the grid, 57% 47% particularly >25% penetration 40% 36% 31% 23% 15% § Carbon-free is the goal 2015 2020 2025 2030 2035 2040 2045 2050 § Intermittency and curtailment are barriers 1,2 California Duck Curve and % Renewable Penetration § 4-hour storage does not efficiently bridge 2013 (10%) 2019 (27%) 25 the duck curve Impact of 15 § Longer duration solutions enable peaker renewables on the grid plant replacements 5 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Hour of day 1 BloombergNEF. CON CONF FIID DEN ENT TIIA AL L 11 2 IEA, “The California Duck Curve”, December 2019. % figures represent solar and wind power penetration in each year. GW

Fortify the Grid for Climate Change Climate change will result in more unpredictable weather events including extreme temperatures, 1 hurricanes and wildfires Texas Freeze ESS batteries operate efficiently in extreme hot and cold weather and still maintain grid stability Texas was seconds away from complete grid failure, which could have taken months to bring back online California Fires ESS batteries are safe for people and the environment: non-flammable and non-toxic Microgrids ESS enables independence 1 Diffenbaugh, N., ‘Verification of extreme event attribution: Using out-of-sample observations to assess changes in probabilities of unprecedented events.’ Science Advances, Vol. 6, No. 12. 18 CON CONF FIID DEN ENT TIIA AL L 12 March 2020.Fortify the Grid for Climate Change Climate change will result in more unpredictable weather events including extreme temperatures, 1 hurricanes and wildfires Texas Freeze ESS batteries operate efficiently in extreme hot and cold weather and still maintain grid stability Texas was seconds away from complete grid failure, which could have taken months to bring back online California Fires ESS batteries are safe for people and the environment: non-flammable and non-toxic Microgrids ESS enables independence 1 Diffenbaugh, N., ‘Verification of extreme event attribution: Using out-of-sample observations to assess changes in probabilities of unprecedented events.’ Science Advances, Vol. 6, No. 12. 18 CON CONF FIID DEN ENT TIIA AL L 12 March 2020.

Strong and Growing Demand for Energy Storage Cumulative Additions to Global Storage Capacity (GWh) Global Total Addressable Market ($bn) Front of the meter Front of the meter +43% 534 CAGR +33% Behind of the meter Behind of the meter CAGR $56 397 $46 301 +44% +32% $39 $28 CAGR CAGR 287 $33 $22 226 $27 $19 199 $22 $18 168 13 $17 $15 130 +34% 121 $14 26 $28 CAGR +42% 233 $24 79 $12 $8 CAGR $20 83 171 $15 39 119 $12 $4 11 52 $8 77 $5 6 26 $4 47 27 5 13 2020 2021 2022 2023 2024 2025 2026 2027 2020 2021 2022 2023 2024 2025 2026 2027 ESS has observed even greater demand from customers than these current analyst estimates Source Guidehouse Insights, ‘Market Data: Utility-Scale Energy Storage Market Update’, 3Q 2020; Guidehouse Insights, ‘Market Data: Energy Storage for Microgrids and Remote Power Systems’, 2Q CON CONF FIID DEN ENT TIIA AL L 13 2020; and Navigant Research, ‘Distributed Energy Storage Overview’, 4Q 2019.Strong and Growing Demand for Energy Storage Cumulative Additions to Global Storage Capacity (GWh) Global Total Addressable Market ($bn) Front of the meter Front of the meter +43% 534 CAGR +33% Behind of the meter Behind of the meter CAGR $56 397 $46 301 +44% +32% $39 $28 CAGR CAGR 287 $33 $22 226 $27 $19 199 $22 $18 168 13 $17 $15 130 +34% 121 $14 26 $28 CAGR +42% 233 $24 79 $12 $8 CAGR $20 83 171 $15 39 119 $12 $4 11 52 $8 77 $5 6 26 $4 47 27 5 13 2020 2021 2022 2023 2024 2025 2026 2027 2020 2021 2022 2023 2024 2025 2026 2027 ESS has observed even greater demand from customers than these current analyst estimates Source Guidehouse Insights, ‘Market Data: Utility-Scale Energy Storage Market Update’, 3Q 2020; Guidehouse Insights, ‘Market Data: Energy Storage for Microgrids and Remote Power Systems’, 2Q CON CONF FIID DEN ENT TIIA AL L 13 2020; and Navigant Research, ‘Distributed Energy Storage Overview’, 4Q 2019.

ESS Wins on Performance 4-12 4h -r12 s hrs 1 16 6+ hrs h+ rs Compelling Performance Operational Flexibility <4 hrs < 4hrs Li-Ion Li-Ion ü Can cycle when needed with no impact to asset life Longer Unlimited cycles, no capacity loss ü Operates at peak efficiency Asset Life 1 6,000 cycles Li-Ion independent of outside environment Superior Ambient -10 C- 60 C °° ü No heating/cooling systems Operating 20-25 C Temperature Li-Ion° needed ü Safe for deployment to urban Non-flammable No Explosion Risk Safety areas or harsh and pristine Li-Ion environments CON CONF FIID DEN ENT TIIA AL L 14 1 Li-Ion cyclability from BYD energy storage system factsheets.ESS Wins on Performance 4-12 4h -r12 s hrs 1 16 6+ hrs h+ rs Compelling Performance Operational Flexibility <4 hrs < 4hrs Li-Ion Li-Ion ü Can cycle when needed with no impact to asset life Longer Unlimited cycles, no capacity loss ü Operates at peak efficiency Asset Life 1 6,000 cycles Li-Ion independent of outside environment Superior Ambient -10 C- 60 C °° ü No heating/cooling systems Operating 20-25 C Temperature Li-Ion° needed ü Safe for deployment to urban Non-flammable No Explosion Risk Safety areas or harsh and pristine Li-Ion environments CON CONF FIID DEN ENT TIIA AL L 14 1 Li-Ion cyclability from BYD energy storage system factsheets.

ESS Wins on Cost 1 Illustrative Cost Comparison Versus Li-Ion How ESS’ Technology Delivers Superior Economics 4 hours 12 hours No scaling Competitive with Li-Ion at 4 hours; ESS wins thereafter $200/kWh $200/kWh Marginal cost of $20/kWh $200/kWh $80/kWh 2 Li-Ion LCOS at 4 hours vs. 12 hours Li-Ion $0.08 $0.07 $0.02 $0.05 0 4 8 12 16 12 hours 4 hours Duration (hours) 1 Figures shown are illustrative. .���������� + .������������������������ + .���������������� + .�� &�� CON CONF FIID DEN ENT TIIA AL L 15 2 Superior economics based on Levelized Cost of Storage (LCOS). �������� = .������������ ������������ ��ℎ�� Capital Cost ($/kWh) Li-IonESS Wins on Cost 1 Illustrative Cost Comparison Versus Li-Ion How ESS’ Technology Delivers Superior Economics 4 hours 12 hours No scaling Competitive with Li-Ion at 4 hours; ESS wins thereafter $200/kWh $200/kWh Marginal cost of $20/kWh $200/kWh $80/kWh 2 Li-Ion LCOS at 4 hours vs. 12 hours Li-Ion $0.08 $0.07 $0.02 $0.05 0 4 8 12 16 12 hours 4 hours Duration (hours) 1 Figures shown are illustrative. .���������� + .������������������������ + .���������������� + .�� &�� CON CONF FIID DEN ENT TIIA AL L 15 2 Superior economics based on Levelized Cost of Storage (LCOS). �������� = .������������ ������������ ��ℎ�� Capital Cost ($/kWh) Li-Ion

ESS Wins on Sustainability Sustainability Focus Areas Raw ingredients of iron, salt and water are Responsibly Sourced Materials earth-abundant 1 Global Warming Potential (GWP) 67% lower CO emissions than Li-Ion 2 Contains no toxic materials and Recyclability 2 requires no special permits for disposal Note GHG impact is dependent on specific Li-Ion chemistry. 1 He, H. et al. “Flow Battery Production: Materials Selection and Environmental Impact.” Journal of Cleaner Production. Vol. 269. 1 October 2020. Noguera, E., Comparative LCA of stand-alone power systems applied to remote cell towers, 2014. CON CON CONF F FIIID D DEN EN ENT T TIIIA A AL L L 16 2 No hazardous materials compliance plan required.ESS Wins on Sustainability Sustainability Focus Areas Raw ingredients of iron, salt and water are Responsibly Sourced Materials earth-abundant 1 Global Warming Potential (GWP) 67% lower CO emissions than Li-Ion 2 Contains no toxic materials and Recyclability 2 requires no special permits for disposal Note GHG impact is dependent on specific Li-Ion chemistry. 1 He, H. et al. “Flow Battery Production: Materials Selection and Environmental Impact.” Journal of Cleaner Production. Vol. 269. 1 October 2020. Noguera, E., Comparative LCA of stand-alone power systems applied to remote cell towers, 2014. CON CON CONF F FIIID D DEN EN ENT T TIIIA A AL L L 16 2 No hazardous materials compliance plan required.

ESS is a Category Defining Technology for Long Duration Storage Vanadium, Sodium Compressed Pumped Li-Ion Li Metal Zinc Bromine Sulfur Air Hydro Low cost at 4 – 12 hours 1 Field proven Earth abundant materials Unlimited cycling Zero capacity fade Wide operational temperature range Environmentally sustainable No fire/ explosion risk Note Internally developed table based on company data and publicly available information. CON CONF FIID DEN ENT TIIA AL L 17 1 Based on our Generation I products, which are no longer deployed.ESS is a Category Defining Technology for Long Duration Storage Vanadium, Sodium Compressed Pumped Li-Ion Li Metal Zinc Bromine Sulfur Air Hydro Low cost at 4 – 12 hours 1 Field proven Earth abundant materials Unlimited cycling Zero capacity fade Wide operational temperature range Environmentally sustainable No fire/ explosion risk Note Internally developed table based on company data and publicly available information. CON CONF FIID DEN ENT TIIA AL L 17 1 Based on our Generation I products, which are no longer deployed.

ESS Technology is Proven and Insured Munich RE Aon One Beacon Insurance 10-year extended Investment-Grade Surety and Corporate Bonding warranty covering Warranty battery modules Growing project surety capacity Warranty continuity Investment-Grade insurance provides Project Insurance additional surety to EXIM customers and financiers “ The ability to ensure battery performance is US Export-Import Bank Qualified a key piece of the puzzle in decarbonizing our energy sector.” Pre-qualified financing available for overseas buyers –Peter Röder, Member of the Board of Management, Munich RE CON CONF FIID DEN ENT TIIA AL L 18ESS Technology is Proven and Insured Munich RE Aon One Beacon Insurance 10-year extended Investment-Grade Surety and Corporate Bonding warranty covering Warranty battery modules Growing project surety capacity Warranty continuity Investment-Grade insurance provides Project Insurance additional surety to EXIM customers and financiers “ The ability to ensure battery performance is US Export-Import Bank Qualified a key piece of the puzzle in decarbonizing our energy sector.” Pre-qualified financing available for overseas buyers –Peter Röder, Member of the Board of Management, Munich RE CON CONF FIID DEN ENT TIIA AL L 18

ESS is Winning in the Market Today Customer in California Customer in Patagonia Use Case Use Case § Microgrid solutions required to mitigate Public Safety § Remote grid served by RoR hydro + diesel gensets Power Shutdown impacts § Storage systems required to minimize genset usage § Li-Ion solutions disqualified due to wildfire risk Why ESS Won Why ESS Won ™ ™ § Energy Warehouse deployed§ 300 kW/2 MWh Energy Warehouse deployed § Best-in-class safety record§ Client abandoned Li-ion RfP after recognizing ESS’ 3x greater peaker replacement capability § Participates in CAISO § $3.1M incremental savings over Li-Ion § Provides local utility grid support during non-PSPS months§ Avoids 12 years of diesel genset emissions NEW PICTURE CON CON CONF F FIIID D DEN EN ENT T TIIIA A AL L L 19ESS is Winning in the Market Today Customer in California Customer in Patagonia Use Case Use Case § Microgrid solutions required to mitigate Public Safety § Remote grid served by RoR hydro + diesel gensets Power Shutdown impacts § Storage systems required to minimize genset usage § Li-Ion solutions disqualified due to wildfire risk Why ESS Won Why ESS Won ™ ™ § Energy Warehouse deployed§ 300 kW/2 MWh Energy Warehouse deployed § Best-in-class safety record§ Client abandoned Li-ion RfP after recognizing ESS’ 3x greater peaker replacement capability § Participates in CAISO § $3.1M incremental savings over Li-Ion § Provides local utility grid support during non-PSPS months§ Avoids 12 years of diesel genset emissions NEW PICTURE CON CON CONF F FIIID D DEN EN ENT T TIIIA A AL L L 19

Technology Overview CON CONF FIID DEN ENT TIIA AL L 20 20Technology Overview CON CONF FIID DEN ENT TIIA AL L 20 20

Technological Breakthrough, Field Proven and Shipping Now Technological R&D roadmap for breakthrough – 1 Iron Flow first conceived But “dirty” electrolyte Field proven ; S200 additional breakthroughs Proton Pump eliminates in 1970s caused rapid degradation shipping now to extend technology power fade and limits on advantage cycle life Technological Success Proven Over Time Innovative Technology Proton 2011 2014 2017 2020 Pump Company formed Demonstrated 10,000+ Gen I EW product line Installed S200 automated operating cycles in the lab launched assembly line Developed lab scale battery Energy Center™ product line launched _ + (+) ELECTRODE: High surface area carbon electrode (-) ELECTRODE: Carbon composite substrate with polypropene spacer 2012 2015 2019 Awarded ARPA-e grant for First commercial deployment S200 commercial battery SEPARATOR: development of Iron based module launched Porous polyethylene separator battery ELECTROLYTE: Ferrous Chloride in aqueous solution CON CONF FIID DEN ENT TIIA AL L 21 1 Based on our Generation I products, which are no longer deployed.Technological Breakthrough, Field Proven and Shipping Now Technological R&D roadmap for breakthrough – 1 Iron Flow first conceived But “dirty” electrolyte Field proven ; S200 additional breakthroughs Proton Pump eliminates in 1970s caused rapid degradation shipping now to extend technology power fade and limits on advantage cycle life Technological Success Proven Over Time Innovative Technology Proton 2011 2014 2017 2020 Pump Company formed Demonstrated 10,000+ Gen I EW product line Installed S200 automated operating cycles in the lab launched assembly line Developed lab scale battery Energy Center™ product line launched _ + (+) ELECTRODE: High surface area carbon electrode (-) ELECTRODE: Carbon composite substrate with polypropene spacer 2012 2015 2019 Awarded ARPA-e grant for First commercial deployment S200 commercial battery SEPARATOR: development of Iron based module launched Porous polyethylene separator battery ELECTROLYTE: Ferrous Chloride in aqueous solution CON CONF FIID DEN ENT TIIA AL L 21 1 Based on our Generation I products, which are no longer deployed.

Robust Intellectual Property Portfolio ESS Critical Technology ESS IP Portfolio (-) (+) Power Module Electrode Electrode 125+ Patents Granted Current Collector and in Pipeline Pending Applications Proton Pump Pressure Plate Undisclosed Number of Trade Secrets and Identified Patents Conductive Porous Separator Separator World-leading Iron Flow expertise, and roadmap to Electrolyte additional breakthroughs and advantages ~57% Employees Have an = Patent 1 Engineering Background protected CON CONF FIID DEN ENT TIIA AL L 22 1 As of March 25, 2021.Robust Intellectual Property Portfolio ESS Critical Technology ESS IP Portfolio (-) (+) Power Module Electrode Electrode 125+ Patents Granted Current Collector and in Pipeline Pending Applications Proton Pump Pressure Plate Undisclosed Number of Trade Secrets and Identified Patents Conductive Porous Separator Separator World-leading Iron Flow expertise, and roadmap to Electrolyte additional breakthroughs and advantages ~57% Employees Have an = Patent 1 Engineering Background protected CON CONF FIID DEN ENT TIIA AL L 22 1 As of March 25, 2021.

Business Overview CON CONF FIID DEN ENT TIIA AL L 23 23Business Overview CON CONF FIID DEN ENT TIIA AL L 23 23

Strong Team Positioned to Grow the Business Management Team CRAIG EVANS ERIC DRESSELHUYS AMIR MOFTAKHAR DR. JULIA SONG Chief Executive Officer President & Founder Chief Financial Officer CTO & Founder (March 2021) HUGH MCDERMOTT MATT BERKEBILE BRIAN LISIECKI RANDY LEWIS Senior Vice President Vice President Vice President Vice President Quality Business Development Operations Business Systems Board of Directors ERIC DRESSELHUYS MICHAEL NIGGLI CRAIG EVANS RICH HOSSFELD Chairman, San Diego Gas President & Founder Chief Executive Officer Board Member, (March 2021) & Electric Co & Entergy SoftBank Energy RAFFI GARABEDIAN SHIRLEY SPEAKMAN KYLE TEAMEY DARYL WILSON Board Member, Board Member, Board Member, Board Member, First Solar Cycle Capital Breakthrough Energy Hydrogenics, ATS Ventures Automation CON CONF FIID DEN ENT TIIA AL L 24Strong Team Positioned to Grow the Business Management Team CRAIG EVANS ERIC DRESSELHUYS AMIR MOFTAKHAR DR. JULIA SONG Chief Executive Officer President & Founder Chief Financial Officer CTO & Founder (March 2021) HUGH MCDERMOTT MATT BERKEBILE BRIAN LISIECKI RANDY LEWIS Senior Vice President Vice President Vice President Vice President Quality Business Development Operations Business Systems Board of Directors ERIC DRESSELHUYS MICHAEL NIGGLI CRAIG EVANS RICH HOSSFELD Chairman, San Diego Gas President & Founder Chief Executive Officer Board Member, (March 2021) & Electric Co & Entergy SoftBank Energy RAFFI GARABEDIAN SHIRLEY SPEAKMAN KYLE TEAMEY DARYL WILSON Board Member, Board Member, Board Member, Board Member, First Solar Cycle Capital Breakthrough Energy Hydrogenics, ATS Ventures Automation CON CONF FIID DEN ENT TIIA AL L 24

One Technology – Two Products of Different Scale Energy Warehouse at Jean Airport ™ ™ Energy Warehouse Energy Center § Behind the meter solution§ Front of the meter solution § 50kW – 90kW configurable range § Customizable configuration range § First commercial deployment in 2015 § Customer trials starting in 2021 § Generation II launched in 2020 § “Battery in a Building” platform § Containerized design for turnkey delivery § Modular design for utility-class § Fast to build and commission CO CON NF FIID DEN ENT TIIA AL L 25One Technology – Two Products of Different Scale Energy Warehouse at Jean Airport ™ ™ Energy Warehouse Energy Center § Behind the meter solution§ Front of the meter solution § 50kW – 90kW configurable range § Customizable configuration range § First commercial deployment in 2015 § Customer trials starting in 2021 § Generation II launched in 2020 § “Battery in a Building” platform § Containerized design for turnkey delivery § Modular design for utility-class § Fast to build and commission CO CON NF FIID DEN ENT TIIA AL L 25

Validated by a Blue-Chip Customer Base Utilities IPPs/Developers Commercial & Industrial EW EC EW EC EW EC § Peaker replacements§ Peaker replacements§ Energy cost savings § T&D upgrade deferrals§ Resource adequacy & grid reliability§ Operational resiliency Demand Drivers § Wildfire resiliency§ 24/7 power supply§ RE integration § Distributed energy services products§ Microgrids§ Carbon footprint reduction/ESG goals Engie Applied Medical Select Customers / Use Cases San Diego Gas & Electric Pacto Energia Duke ConEdison ČEZ Group Enel Honeywell Idimax Energy Energy Grupo Starwood Select Pipeline Naturgy Marathon SAESA Energy PacifiCorp CO CON NF FIID DEN ENT TIIA AL L 26 Note “EW” refers to Energy Warehouse™, “EC” refers to Energy Center™.Validated by a Blue-Chip Customer Base Utilities IPPs/Developers Commercial & Industrial EW EC EW EC EW EC § Peaker replacements§ Peaker replacements§ Energy cost savings § T&D upgrade deferrals§ Resource adequacy & grid reliability§ Operational resiliency Demand Drivers § Wildfire resiliency§ 24/7 power supply§ RE integration § Distributed energy services products§ Microgrids§ Carbon footprint reduction/ESG goals Engie Applied Medical Select Customers / Use Cases San Diego Gas & Electric Pacto Energia Duke ConEdison ČEZ Group Enel Honeywell Idimax Energy Energy Grupo Starwood Select Pipeline Naturgy Marathon SAESA Energy PacifiCorp CO CON NF FIID DEN ENT TIIA AL L 26 Note “EW” refers to Energy Warehouse™, “EC” refers to Energy Center™.

Strategy to Scale Globally ESS’ ability to grow is supported by ü Relationships in Europe and Asia-Pacific Manufacturing Capacity (MWh) ü Automated manufacturing process ~16,000 ü Supply chain of readily sourced components and raw materials ~10,000 ~5,000 ~2,000 ~150 2021 2022 2023 2024 2025 2026 150,000 sq. ft. Strategic investments Australia Australia Europe Power manufacturing in supply chain to manufacturing go- manufacturing go-live Module facility in Oregon grow capacity live for EW with LOI for EC and Power manufacturing on Brisbane facility Module go-live Robotic automation Roll out of redesigned cell designed and automation cells Europe manufacturing Vertically integrate built by ESS (2x efficiency) go-live for EC and EW power module comportments CON CONF FIID DEN ENT TIIA AL L 27Strategy to Scale Globally ESS’ ability to grow is supported by ü Relationships in Europe and Asia-Pacific Manufacturing Capacity (MWh) ü Automated manufacturing process ~16,000 ü Supply chain of readily sourced components and raw materials ~10,000 ~5,000 ~2,000 ~150 2021 2022 2023 2024 2025 2026 150,000 sq. ft. Strategic investments Australia Australia Europe Power manufacturing in supply chain to manufacturing go- manufacturing go-live Module facility in Oregon grow capacity live for EW with LOI for EC and Power manufacturing on Brisbane facility Module go-live Robotic automation Roll out of redesigned cell designed and automation cells Europe manufacturing Vertically integrate built by ESS (2x efficiency) go-live for EC and EW power module comportments CON CONF FIID DEN ENT TIIA AL L 27

97% Less Capital Required – Ready to Scale Globally Simple, automated Simple, Low-cost Production in the USA ESS manufacturing line $in millions/GWh of Battery Module Production Capacity ~$140 Expensive, complex Li-Ion battery manufacturing line ~$4 Li-Ion competitor CON CONF FIID DEN ENT TIIA AL L 28 Source Lux Research.97% Less Capital Required – Ready to Scale Globally Simple, automated Simple, Low-cost Production in the USA ESS manufacturing line $in millions/GWh of Battery Module Production Capacity ~$140 Expensive, complex Li-Ion battery manufacturing line ~$4 Li-Ion competitor CON CONF FIID DEN ENT TIIA AL L 28 Source Lux Research.

Capital Investment Will Enable Rapid Expansion Increase Expand Sales Footprint Net Cash for Growth Hire new sales team members and Manufacturing Capacity expand production footprint into 1 Fully funds capital plan to increase ~$493m Europe and Australia capacity from >250MWh in 2021 to 16GWh by 2025 ™ Launch Energy Center Strengthen Balance Sheet Deploy product that is optimized for Supports credit requirements to the fast-growing utility-scale storage convert large projects in pipeline segment Further Extend Technology Advantage Higher performance electrolyte to enable an 85% reduction in cost per megawatt hour by 2025 1 PF 12/31/2020 net cash assumes funding of $27.5m of C-2 raise, of which $16m has yet to be funded; amount is expected to be funded prior to transaction close. Net cash also includes $1.5m CO CO CO CON N N NF F F FIIIID D D DEN EN EN ENT T T TIIIIA A A AL L L L 29 of restricted cash. For additional information, please refer to the Detailed Transaction Overview on p. 36 of this presentation.Capital Investment Will Enable Rapid Expansion Increase Expand Sales Footprint Net Cash for Growth Hire new sales team members and Manufacturing Capacity expand production footprint into 1 Fully funds capital plan to increase ~$493m Europe and Australia capacity from >250MWh in 2021 to 16GWh by 2025 ™ Launch Energy Center Strengthen Balance Sheet Deploy product that is optimized for Supports credit requirements to the fast-growing utility-scale storage convert large projects in pipeline segment Further Extend Technology Advantage Higher performance electrolyte to enable an 85% reduction in cost per megawatt hour by 2025 1 PF 12/31/2020 net cash assumes funding of $27.5m of C-2 raise, of which $16m has yet to be funded; amount is expected to be funded prior to transaction close. Net cash also includes $1.5m CO CO CO CON N N NF F F FIIIID D D DEN EN EN ENT T T TIIIIA A A AL L L L 29 of restricted cash. For additional information, please refer to the Detailed Transaction Overview on p. 36 of this presentation.

Financial Forecast CON CONF FIID DEN ENT TIIA AL L 30 30Financial Forecast CON CONF FIID DEN ENT TIIA AL L 30 30

High Quality Pipeline ™ Projected Pipeline for Energy Center Global Identified Opportunities ™ and Energy Warehouse Qualifying Negotiating Qualifying 28% 40% Booked 100% Awarded Negotiating Negotiating 66% 40% Awarded Awarded Booked 20% 6% 5% ™ Energy Center Opportunities 2021E 2022E 2023E ™ Energy Warehouse Opportunities $2 Million $37 Million $300 Million $7+ Billion Pipeline for Continued Growth in Outer Years CON CONF FIID DEN ENT TIIA AL L 31High Quality Pipeline ™ Projected Pipeline for Energy Center Global Identified Opportunities ™ and Energy Warehouse Qualifying Negotiating Qualifying 28% 40% Booked 100% Awarded Negotiating Negotiating 66% 40% Awarded Awarded Booked 20% 6% 5% ™ Energy Center Opportunities 2021E 2022E 2023E ™ Energy Warehouse Opportunities $2 Million $37 Million $300 Million $7+ Billion Pipeline for Continued Growth in Outer Years CON CONF FIID DEN ENT TIIA AL L 31

ESS’ Robust Revenue Growth Projected Revenue by Product Offering ($in millions) § Growth accelerates as Energy $3,562 Center deployments start in EC EW EF Services 2023 $2,572 § Forecast driven by identified pipeline of near-term opportunities $1,645 § ESS expansion into Australia (2023) and Europe (2024) $803 supports continued growth $300 § Energy Franchise lease and $37 $2 Services revenue streams become bigger contributors 2021E 2022E 2023E 2024E 2025E 2026E 2027E as ESS expands Market 0% 0% 1% 2% 4% 6% Share % CON CONF FIID DEN ENT TIIA AL L 32 Note Total addressable market value for the microgrid, distributed energy and utility industries from Guidehouse Insights.ESS’ Robust Revenue Growth Projected Revenue by Product Offering ($in millions) § Growth accelerates as Energy $3,562 Center deployments start in EC EW EF Services 2023 $2,572 § Forecast driven by identified pipeline of near-term opportunities $1,645 § ESS expansion into Australia (2023) and Europe (2024) $803 supports continued growth $300 § Energy Franchise lease and $37 $2 Services revenue streams become bigger contributors 2021E 2022E 2023E 2024E 2025E 2026E 2027E as ESS expands Market 0% 0% 1% 2% 4% 6% Share % CON CONF FIID DEN ENT TIIA AL L 32 Note Total addressable market value for the microgrid, distributed energy and utility industries from Guidehouse Insights.

ESS Delivers Compelling Profitability Projected Gross Margin ($in millions) Projected EBITDA ($in millions) $1,332 $1,059 $950 $739 $508 $360 $217 $131 $47 ($13) ($20) ($2) ($43) $2 2021E 2022E 2023E 2024E 2025E 2026E 2027E 2021E 2022E 2023E 2024E 2025E 2026E 2027E 16% 27% 31% 37% 37% 1% 16% 22% 29% 30% % Margin % Margin CON CONF FIID DEN ENT TIIA AL L 33ESS Delivers Compelling Profitability Projected Gross Margin ($in millions) Projected EBITDA ($in millions) $1,332 $1,059 $950 $739 $508 $360 $217 $131 $47 ($13) ($20) ($2) ($43) $2 2021E 2022E 2023E 2024E 2025E 2026E 2027E 2021E 2022E 2023E 2024E 2025E 2026E 2027E 16% 27% 31% 37% 37% 1% 16% 22% 29% 30% % Margin % Margin CON CONF FIID DEN ENT TIIA AL L 33

Potential Upside to Business Plan New US federal and state policies on infrastructure, decarbonization and national security Emerging mandates in EU and Asia-Pacific on decarbonization and storage Demand impact of USTDA, Power Africa, UNDP and World Bank targets Further economies of scale and technology enhancements Additional revenue streams (e.g., Storage as a Service, Warranty) CON CON CON CONF F F FIIIID D D DEN EN EN ENT T T TIIIIA A A AL L L L 34Potential Upside to Business Plan New US federal and state policies on infrastructure, decarbonization and national security Emerging mandates in EU and Asia-Pacific on decarbonization and storage Demand impact of USTDA, Power Africa, UNDP and World Bank targets Further economies of scale and technology enhancements Additional revenue streams (e.g., Storage as a Service, Warranty) CON CON CON CONF F F FIIIID D D DEN EN EN ENT T T TIIIIA A A AL L L L 34

Valuation Overview CON CONF FIID DEN ENT TIIA AL L 35 35Valuation Overview CON CONF FIID DEN ENT TIIA AL L 35 35

Detailed Transaction Overview Transaction Overview Illustrative Pro Forma Valuation and Sources & Uses ($ in millions, except per share data; shares in millions) Total Enterprise Value Summary § Pro forma enterprise value of $1,072 million (0.7x 2025E Revenue) Pro forma shares outstanding 156.5 § $465 million cash proceeds inclusive of $250 million PIPE proceeds (x) ESS share price $10.00 1 and transaction expenses assuming zero redemptions Pro Forma Equity Value $1,565 2 1,2 (-) Current cash (28) § Pro forma net cash of $493 million 1 (-) Net proceeds (465) 2 § Inclusive of $28 million existing net cash on balance sheet Pro Forma Enterprise Value $1,072 § ESS shareholders are rolling 100% of equity ownership Metric Multiple Valuation Multiples EV / 2025E Revenue $1,645 0.7x 1,2,3 EV / 2025E EBITDA $360 3.0x Pro Forma Ownership @ $10.00 per share Sources $ % Shares Founder shares Rollover equity 1,003 64% 100.3 ACON S2 cash in trust 250 16% 25.0 4% 1 PIPE investment 250 16% 25.0 PIPE investors Founder Shares 63 4% 6.3 16% Total sources $1,565 100% 156.5 ESS existing Uses $ % Rollover equity 1,003 64% shareholders ACON S2 public Cash to balance sheet 465 30% 64% Founder shares 63 4% shareholders Estimated fees and expenses 35 2% 16% Total uses $1,565 100% Note Figures may not sum due to rounding. 1 SB Energy Global Holdings Limited and Breakthrough Energy Ventures, LLC, existing equity investors in ESS, have indicated an interest in investing an aggregate of $51.5 million in the offering. These existing investors are expected to agree to reduce the amount of their existing option to invest in the C-2 raise to an aggregate of $16 million, which amount would be invested (if such option is exercised) immediately prior to the closing of the offering. In exchange for this agreement, such investors would receive warrants to purchase an aggregate of 14,364,222 shares of ESS Series C-2 preferred stock at an exercise price of $0.001 per share, which warrants would automatically be net-exercised immediately prior to the closing of the offering or terminate unexercised if the offering does not close. 2 Pro forma 12/31/2020 net cash assumes funding of an aggregate of $27.5 million in the C-2 raise, of which $11.5 million has been funded and $16 million is expected to be funded by SB Energy Global Holdings Limited and Breakthrough Energy Ventures, LLC, as described in the footnote above. Net cash also includes $1.5 million of restricted cash. CO CON NF FIID DEN ENT TIIA AL L 36 3 Additional dilutive securities include 8.3m ACON S2 public warrants, 4.1m founder warrants and $165m shareholder earnout.Detailed Transaction Overview Transaction Overview Illustrative Pro Forma Valuation and Sources & Uses ($ in millions, except per share data; shares in millions) Total Enterprise Value Summary § Pro forma enterprise value of $1,072 million (0.7x 2025E Revenue) Pro forma shares outstanding 156.5 § $465 million cash proceeds inclusive of $250 million PIPE proceeds (x) ESS share price $10.00 1 and transaction expenses assuming zero redemptions Pro Forma Equity Value $1,565 2 1,2 (-) Current cash (28) § Pro forma net cash of $493 million 1 (-) Net proceeds (465) 2 § Inclusive of $28 million existing net cash on balance sheet Pro Forma Enterprise Value $1,072 § ESS shareholders are rolling 100% of equity ownership Metric Multiple Valuation Multiples EV / 2025E Revenue $1,645 0.7x 1,2,3 EV / 2025E EBITDA $360 3.0x Pro Forma Ownership @ $10.00 per share Sources $ % Shares Founder shares Rollover equity 1,003 64% 100.3 ACON S2 cash in trust 250 16% 25.0 4% 1 PIPE investment 250 16% 25.0 PIPE investors Founder Shares 63 4% 6.3 16% Total sources $1,565 100% 156.5 ESS existing Uses $ % Rollover equity 1,003 64% shareholders ACON S2 public Cash to balance sheet 465 30% 64% Founder shares 63 4% shareholders Estimated fees and expenses 35 2% 16% Total uses $1,565 100% Note Figures may not sum due to rounding. 1 SB Energy Global Holdings Limited and Breakthrough Energy Ventures, LLC, existing equity investors in ESS, have indicated an interest in investing an aggregate of $51.5 million in the offering. These existing investors are expected to agree to reduce the amount of their existing option to invest in the C-2 raise to an aggregate of $16 million, which amount would be invested (if such option is exercised) immediately prior to the closing of the offering. In exchange for this agreement, such investors would receive warrants to purchase an aggregate of 14,364,222 shares of ESS Series C-2 preferred stock at an exercise price of $0.001 per share, which warrants would automatically be net-exercised immediately prior to the closing of the offering or terminate unexercised if the offering does not close. 2 Pro forma 12/31/2020 net cash assumes funding of an aggregate of $27.5 million in the C-2 raise, of which $11.5 million has been funded and $16 million is expected to be funded by SB Energy Global Holdings Limited and Breakthrough Energy Ventures, LLC, as described in the footnote above. Net cash also includes $1.5 million of restricted cash. CO CON NF FIID DEN ENT TIIA AL L 36 3 Additional dilutive securities include 8.3m ACON S2 public warrants, 4.1m founder warrants and $165m shareholder earnout.

Selected Public Comparable Universe Battery Storage Fuel Cell and Electrolyzers Renewable Technologies Supporting Supporting Supporting Considerations Considerations Considerations Characteristics Characteristics Characteristics ü Growth stage û Primarily ü Technology û Not reliant on ü Growth is tied û Part of solar battery lithium-ion with long- battery directly to supply chain companies technologies duration technology significantly and not reliant storage increasing on battery û Focused on û Significantly applications renewable technology short-duration less efficient penetration or EV end markets CON CONF FIID DEN ENT TIIA AL L 37Selected Public Comparable Universe Battery Storage Fuel Cell and Electrolyzers Renewable Technologies Supporting Supporting Supporting Considerations Considerations Considerations Characteristics Characteristics Characteristics ü Growth stage û Primarily ü Technology û Not reliant on ü Growth is tied û Part of solar battery lithium-ion with long- battery directly to supply chain companies technologies duration technology significantly and not reliant storage increasing on battery û Focused on û Significantly applications renewable technology short-duration less efficient penetration or EV end markets CON CONF FIID DEN ENT TIIA AL L 37

Selected Operational Benchmarking Battery Storage Fuel Cell and Electrolyzers Renewable Technologies Average: 58% Average: 25% Average: 121% 594.5% 170.4% 105.8% 72.0% 53.7% 47.3% 43.4% 23.8% 15.3% 17.2% NM Average: 31% Average: 26% Average: 32% 40.7% 37.4% 35.3% 33.4% 31.3% 30.3% 25.0% 24.3% 22.5% 21.4% NM 2027E 2027E 2024E 2024E 2024E 2024E 2024E 2024E 2021E 2021E 2021E Average: 22% Average: 15% Average: 23% 32.8% 29.7% 27.3% 25.2% 19.8% 19.2% 16.0% 15.0% 15.6% 14.5% 10.5% 2027E 2027E 2024E 2024E 2024E 2024E 2024E 2024E 2021E 2021E 2021E Source Company management, public filings and FactSet as of April 28, 2021. Note QuantumScape, Stem and EOS revenues, gross income and EBITDA based on company investor presentations. CON CONF FIID DEN ENT TIIA AL L 38 NM denotes not meaningful or negative. EBITDA margin Gross margin Revenue CAGR ’21-24Selected Operational Benchmarking Battery Storage Fuel Cell and Electrolyzers Renewable Technologies Average: 58% Average: 25% Average: 121% 594.5% 170.4% 105.8% 72.0% 53.7% 47.3% 43.4% 23.8% 15.3% 17.2% NM Average: 31% Average: 26% Average: 32% 40.7% 37.4% 35.3% 33.4% 31.3% 30.3% 25.0% 24.3% 22.5% 21.4% NM 2027E 2027E 2024E 2024E 2024E 2024E 2024E 2024E 2021E 2021E 2021E Average: 22% Average: 15% Average: 23% 32.8% 29.7% 27.3% 25.2% 19.8% 19.2% 16.0% 15.0% 15.6% 14.5% 10.5% 2027E 2027E 2024E 2024E 2024E 2024E 2024E 2024E 2021E 2021E 2021E Source Company management, public filings and FactSet as of April 28, 2021. Note QuantumScape, Stem and EOS revenues, gross income and EBITDA based on company investor presentations. CON CONF FIID DEN ENT TIIA AL L 38 NM denotes not meaningful or negative. EBITDA margin Gross margin Revenue CAGR ’21-24

Selected Valuation Benchmarking Battery Storage Fuel Cell and Electrolyzers Renewable Technologies Average: 3.3x Average: 9.8x Average: 12.1x 24.6x 14.6x 14.2x 7.8x 7.6x 4.7x 4.6x 3.8x 2.8x 0.7x 0.6x 2025E 2027E 2024E 2024E 2024E 2024E 2024E 2024E 2021E 2021E 2021E Average: 46.5x Average: 13.3x Average: 72.9x 135.2x 100.1x 75.1x 40.6x 38.1x 23.7x 18.8x 18.3x 16.9x 4.3x 3.0x 2025E 2027E 2024E 2024E 2024E 2024E 2024E 2024E 2021E 2021E 2021E Source Company management, public filings and FactSet as of April 28, 2021. Note QuantumScape, Stem and EOS revenues, gross income and EBITDA based on company investor presentations. CON CONF FIID DEN ENT TIIA AL L 39 EV / EBITDA EV / RevenueSelected Valuation Benchmarking Battery Storage Fuel Cell and Electrolyzers Renewable Technologies Average: 3.3x Average: 9.8x Average: 12.1x 24.6x 14.6x 14.2x 7.8x 7.6x 4.7x 4.6x 3.8x 2.8x 0.7x 0.6x 2025E 2027E 2024E 2024E 2024E 2024E 2024E 2024E 2021E 2021E 2021E Average: 46.5x Average: 13.3x Average: 72.9x 135.2x 100.1x 75.1x 40.6x 38.1x 23.7x 18.8x 18.3x 16.9x 4.3x 3.0x 2025E 2027E 2024E 2024E 2024E 2024E 2024E 2024E 2021E 2021E 2021E Source Company management, public filings and FactSet as of April 28, 2021. Note QuantumScape, Stem and EOS revenues, gross income and EBITDA based on company investor presentations. CON CONF FIID DEN ENT TIIA AL L 39 EV / EBITDA EV / Revenue

Transaction Priced at a Discount to Peer Multiples Implied EV Based on Selected Comparable Companies Trading Transaction Value ($ in millions; implied future and discounted EV rounded to the nearest $5m) Implied Future EV Implied Discounted EV Implied Post-Money EV $8,225 84% discount $3,965 $4,935 66% discount $1,072 $2,380 Implied Multiples EV/2025E Revenue 3.0x – 5.0x 1.4x – 2.4x 0.7x EV/2025E EBITDA 13.7x – 22.9x 6.6x – 11.0x 3.0x § Using a future valuation date of 6/30/2025, ESS is valued by applying 2025E revenue of $1,645m to an EV/CY’21E revenue multiple of 3.0 – 5.0x based on peer multiples, resulting in an implied future EV of $6,580m at the midpoint § The implied future EV is then discounted at a 20% rate over a 4 year period to arrive at an implied present value of $3,173m at Valuation Approach 1 the midpoint § Transaction priced at a substantial discount Note Company projections. CON CONF FIID DEN ENT TIIA AL L 40 1 Assumes a 20% discount rate; based on midpoint of implied future enterprise value of $6,580m.Transaction Priced at a Discount to Peer Multiples Implied EV Based on Selected Comparable Companies Trading Transaction Value ($ in millions; implied future and discounted EV rounded to the nearest $5m) Implied Future EV Implied Discounted EV Implied Post-Money EV $8,225 84% discount $3,965 $4,935 66% discount $1,072 $2,380 Implied Multiples EV/2025E Revenue 3.0x – 5.0x 1.4x – 2.4x 0.7x EV/2025E EBITDA 13.7x – 22.9x 6.6x – 11.0x 3.0x § Using a future valuation date of 6/30/2025, ESS is valued by applying 2025E revenue of $1,645m to an EV/CY’21E revenue multiple of 3.0 – 5.0x based on peer multiples, resulting in an implied future EV of $6,580m at the midpoint § The implied future EV is then discounted at a 20% rate over a 4 year period to arrive at an implied present value of $3,173m at Valuation Approach 1 the midpoint § Transaction priced at a substantial discount Note Company projections. CON CONF FIID DEN ENT TIIA AL L 40 1 Assumes a 20% discount rate; based on midpoint of implied future enterprise value of $6,580m.

Energy Storage for a Cleaner FutureEnergy Storage for a Cleaner Future

Appendix CON CONF FIID DEN ENT TIIA AL L 42 42Appendix CON CONF FIID DEN ENT TIIA AL L 42 42

PF Summary Financials Values in 000s 2021 2022 2023 2024 2025 2026 2027 Revenue Product - EW Purchase & Lease $2,381 $22,679 $34,520 $47,203 $66,328 $94,808 $135,248 Product - EC Purchase– $14,224 $256,249 $696,998 $1,447,504 $2,222,420 $2,986,242 Product - EF Purchase–– $4,177 $28,696 $41,797 $50,522 $61,113 Service Agreement $15 $314 $5,535 $29,808 $88,884 $203,964 $379,833 Total Revenue $2,396 $37,217 $300,481 $802,704 $1,644,513 $2,571,715 $3,562,436 Market Share (%) 0% 0% 1% 2% 4% 6% 6% Cost of Goods Sold $4,560 $50,424 $253,087 $585,929 $1,136,469 $1,622,129 $2,229,953 Gross Profit ($2,163) ($13,207) $47,393 $216,776 $508,044 $949,586 $1,332,483 Gross Margin (%) NM NM 16% 27% 31% 37% 37% Total Operating Expense $17,659 $29,854 $45,841 $86,264 $148,230 $210,718 $273,590 EBITDA ($19,822) ($43,062) $1,552 $130,511 $359,813 $738,868 $1,058,894 Margin (%) NM NM 1% 16% 22% 29% 30% Depreciation $432 $4,712 $17,737 $32,842 $46,508 $63,580 $69,824 Interest Expense– $59 $287 $414 $530 $656 $817 Taxes (net of NOL)–––– $56,715 $141,673 $207,533 Net Income (Loss) ($20,255) ($47,833) ($16,472) $97,255 $256,061 $532,959 $780,720 NM NM NM 12% 16% 21% 22% CapEx Maintenance CapEx ($3,259) ($8,240) ($8,487) ($8,742) ($9,004) ($9,274) ($9,552) Leased Equipment– ($7,980) ($6,680) ($6,532) ($8,100) ($10,270) ($13,875) Manfacturing Capacity Growth CapEx ($500) ($21,200) ($49,000) ($93,500) ($31,500) ($87,000) ($124,162) Total CapEx ($3,759) ($37,420) ($64,167) ($108,774) ($48,604) ($106,544) ($147,589) Portion of Revenue (%) 157% 101% 21% 14% 3% 4% 4% EBITDA - CapEx ($23,581) ($80,482) ($62,615) $21,738 $311,209 $632,324 $911,305 CFO - CapEx ($21,145) ($84,544) ($97,759) ($49,913) $151,619 $409,416 $664,954 Cash on Balance Sheet $470,816 $390,967 $296,708 $249,857 $405,087 $818,909 $1,489,775 Number of Units Sold 2021 2022 2023 2024 2025 2026 2027 Product - EW Purchase 27 179 200 252 376 552 824 Product - EW Lease– 40 40 48 64 84 120 1 Product - EC Purchase– 33 600 1,571 3,433 5,379 7,449 CON CONF FIID DEN ENT TIIA AL L 43 1 Number of units sold refers to number of powertrains sold; Energy Centers are expected to contain multiple powertrains.PF Summary Financials Values in 000s 2021 2022 2023 2024 2025 2026 2027 Revenue Product - EW Purchase & Lease $2,381 $22,679 $34,520 $47,203 $66,328 $94,808 $135,248 Product - EC Purchase– $14,224 $256,249 $696,998 $1,447,504 $2,222,420 $2,986,242 Product - EF Purchase–– $4,177 $28,696 $41,797 $50,522 $61,113 Service Agreement $15 $314 $5,535 $29,808 $88,884 $203,964 $379,833 Total Revenue $2,396 $37,217 $300,481 $802,704 $1,644,513 $2,571,715 $3,562,436 Market Share (%) 0% 0% 1% 2% 4% 6% 6% Cost of Goods Sold $4,560 $50,424 $253,087 $585,929 $1,136,469 $1,622,129 $2,229,953 Gross Profit ($2,163) ($13,207) $47,393 $216,776 $508,044 $949,586 $1,332,483 Gross Margin (%) NM NM 16% 27% 31% 37% 37% Total Operating Expense $17,659 $29,854 $45,841 $86,264 $148,230 $210,718 $273,590 EBITDA ($19,822) ($43,062) $1,552 $130,511 $359,813 $738,868 $1,058,894 Margin (%) NM NM 1% 16% 22% 29% 30% Depreciation $432 $4,712 $17,737 $32,842 $46,508 $63,580 $69,824 Interest Expense– $59 $287 $414 $530 $656 $817 Taxes (net of NOL)–––– $56,715 $141,673 $207,533 Net Income (Loss) ($20,255) ($47,833) ($16,472) $97,255 $256,061 $532,959 $780,720 NM NM NM 12% 16% 21% 22% CapEx Maintenance CapEx ($3,259) ($8,240) ($8,487) ($8,742) ($9,004) ($9,274) ($9,552) Leased Equipment– ($7,980) ($6,680) ($6,532) ($8,100) ($10,270) ($13,875) Manfacturing Capacity Growth CapEx ($500) ($21,200) ($49,000) ($93,500) ($31,500) ($87,000) ($124,162) Total CapEx ($3,759) ($37,420) ($64,167) ($108,774) ($48,604) ($106,544) ($147,589) Portion of Revenue (%) 157% 101% 21% 14% 3% 4% 4% EBITDA - CapEx ($23,581) ($80,482) ($62,615) $21,738 $311,209 $632,324 $911,305 CFO - CapEx ($21,145) ($84,544) ($97,759) ($49,913) $151,619 $409,416 $664,954 Cash on Balance Sheet $470,816 $390,967 $296,708 $249,857 $405,087 $818,909 $1,489,775 Number of Units Sold 2021 2022 2023 2024 2025 2026 2027 Product - EW Purchase 27 179 200 252 376 552 824 Product - EW Lease– 40 40 48 64 84 120 1 Product - EC Purchase– 33 600 1,571 3,433 5,379 7,449 CON CONF FIID DEN ENT TIIA AL L 43 1 Number of units sold refers to number of powertrains sold; Energy Centers are expected to contain multiple powertrains.

ACON S2 Overview Strategic Sustainability Platform for Success § ACON S2 Acquisition Corp. (NASDAQ: STWO) ü Domain Expertiseü Public Markets § $250mm IPO in September 2020 ü Sustainabilityü Governance § Criteria: authentic sustainability leader, significant value creation potential, strong competitive ü Global Networkü Capital Formation position, at an inflection point, experienced team § 25 years of investing, AUM of ~$6B § Over 70 investments since inception § 31 active portfolio companies employing A Perfect Fit for the ACON S2 Mission over 39,000 people across 32 countries CON CONF FIID DEN ENT TIIA AL L 44ACON S2 Overview Strategic Sustainability Platform for Success § ACON S2 Acquisition Corp. (NASDAQ: STWO) ü Domain Expertiseü Public Markets § $250mm IPO in September 2020 ü Sustainabilityü Governance § Criteria: authentic sustainability leader, significant value creation potential, strong competitive ü Global Networkü Capital Formation position, at an inflection point, experienced team § 25 years of investing, AUM of ~$6B § Over 70 investments since inception § 31 active portfolio companies employing A Perfect Fit for the ACON S2 Mission over 39,000 people across 32 countries CON CONF FIID DEN ENT TIIA AL L 44

™ Energy Warehouse Overview Product Summary Product Deployments § Behind the meter solution § Containerized design for turnkey delivery § First commercial deployment in 2015 § Fast to build and commission § Generation II launched in 2020 Current Specifications Stone Edge Farms USACE UCSD (CA) 10 kW/60 kWh; 2015 60 kW/225 kWh; 2016 50 kW /400 kWh; 2017 Configurable Range: 50kW – 90kW (peak power) Storage Duration: 4 – 12 hours Usable Energy: 400kWh – 600kWh Response Time: <1 second Module Cycle Life: >20,000 cycles Ambient Temperature: -5°C to +50°C DNV-GL (TX) Camp Pendleton US Utility Expected Life: 25 year service life 50 kW /400 kWh ; 2017 50 kW /400 kWh; 2018 50 kW /400 kWh; 2020 Warranty: 1 yr comprehensive, 10 yr warranty backstop from Munich Re available CO CON NF FIID DEN ENT TIIA AL L 45™ Energy Warehouse Overview Product Summary Product Deployments § Behind the meter solution § Containerized design for turnkey delivery § First commercial deployment in 2015 § Fast to build and commission § Generation II launched in 2020 Current Specifications Stone Edge Farms USACE UCSD (CA) 10 kW/60 kWh; 2015 60 kW/225 kWh; 2016 50 kW /400 kWh; 2017 Configurable Range: 50kW – 90kW (peak power) Storage Duration: 4 – 12 hours Usable Energy: 400kWh – 600kWh Response Time: <1 second Module Cycle Life: >20,000 cycles Ambient Temperature: -5°C to +50°C DNV-GL (TX) Camp Pendleton US Utility Expected Life: 25 year service life 50 kW /400 kWh ; 2017 50 kW /400 kWh; 2018 50 kW /400 kWh; 2020 Warranty: 1 yr comprehensive, 10 yr warranty backstop from Munich Re available CO CON NF FIID DEN ENT TIIA AL L 45

™ Energy Center Overview Product Summary § Front of the meter solution§ Modular design for utility- class § Customer trials starting in 2021§ Power capacities starting at 3MW § “Battery in a Building” platform Building Blocks for Existing Products Current Specifications Configurable Range: Customizable Quad Pods Storage Duration: 6 -12 hours Usable Energy: Customizable Response Time: <1 second Module Cycle Life: >20,000 cycles Ambient Temperature: -40°C to +50°C Power Train Expected Life: 25 year service life Warranty: 10-year battery module, extended warranty to 25 years available CON CONF FIID DEN ENT TIIA AL L 46™ Energy Center Overview Product Summary § Front of the meter solution§ Modular design for utility- class § Customer trials starting in 2021§ Power capacities starting at 3MW § “Battery in a Building” platform Building Blocks for Existing Products Current Specifications Configurable Range: Customizable Quad Pods Storage Duration: 6 -12 hours Usable Energy: Customizable Response Time: <1 second Module Cycle Life: >20,000 cycles Ambient Temperature: -40°C to +50°C Power Train Expected Life: 25 year service life Warranty: 10-year battery module, extended warranty to 25 years available CON CONF FIID DEN ENT TIIA AL L 46