Summary of Significant Accounting Policies (Details Textual) - USD ($)	1 Months Ended		2 Months Ended	3 Months Ended		6 Months Ended		12 Months Ended
	May 22, 2020	Feb. 29, 2020	Feb. 14, 2020	Jun. 30, 2020		Jun. 30, 2020		Dec. 31, 2019		Dec. 31, 2018	Mar. 31, 2020	[1]	Jun. 30, 2019		Jun. 04, 2019	Jun. 02, 2019	[2]
Summary of Significant Accounting Policies (Textual)
Common stock, shares, issued															10,000
Insurance coverage						$ 250,000
Public Offering				$ 476,189		476,189
Underwriter discount						3,500,000
Tangible assets				5,000,001		5,000,001
Stock split, description			The Company completed a stock split of 1 to 575 shares of Class B common stock, resulting in 5,750,000 shares of Class B common stock issued and outstanding.
Federal depository insurance coverage			$ 250,000
Total assets			50,001	177,515,829		177,515,829		$ 1
Total cash and cash equivalents			50,000	496,557		496,557
Total liabilities			50,325	78,038		78,038		278
Contingently redeemable preferred stock
Total members deficit			$ (324)	5,000,006		5,000,006		(277)	[1]		$ (731)		$ 1			$ 1
EOS ENERGY STORAGE, LLC [Member]
Summary of Significant Accounting Policies (Textual)
Total assets				9,312,000		9,312,000		13,057,000		$ 15,046,000
Total cash and cash equivalents				920,000		920,000		862,000		5,498,000
Total liabilities				98,369,000		98,369,000		87,414,000		13,872,000
Convertible notes payable				85,636,000		85,636,000		76,559,000		2,350,000
Contingently redeemable preferred stock				109,841,000		109,841,000		109,365,000
Total members deficit				$ (198,898,000)		$ (198,898,000)		$ (183,722,000)		(104,374,000)
Business combination, description						The Company entered into a letter of intent dated June 24, 2020 to merge with B. Riley Principal Merger Corp. II (“BMRG II”). BMRG II is a special acquisition company (“SPAC”) incorporated for the purpose of effecting a merger, capital stock exchange, asset acquisition, stock purchase, reorganization or similar business combination with one or more businesses (the “SPAC transaction”). The SPAC transaction is currently expected to close in October 2020 and would allow all holders of the Company’s equity and equity-linked securities to receive a combination of common stock of the continuing public company, which will be a wholly owned subsidiary of BMRG II. Accordingly, as part of the closing of the SPAC transaction, the Company currently expects substantially all the total amounts owed on the Company’s outstanding convertible notes will be converted into shares of the continuing public company. The merger would result in a net increase in cash to the Company of between approximately $66.4 million, assuming maximum shareholder redemptions permitted under the Business Combination Agreement, and $212.3 million, assuming minimum shareholder redemption, for which management plans to use to, among other things, fund the Company’s obligations as they become due. While management believes they will be able to close the SPAC transaction in the fourth quarter of 2020, no assurance can be provided that such transaction will close or on terms that are acceptable to the Company. If the Company is unable to close the SPAC transaction, management plans to obtain additional outside capital to fund the Company’s current cost structure through the issuance of Series E Preferred shares and modify the terms of the Company’s outstanding convertible notes to, among other things, extend the current amounts owed to future periods. While management believes they would be able to issue Series E Preferred shares and modify the terms of the Company’s outstanding convertible notes in the event the SPAC transaction fails to close, no assurance can be provided that such issuance and modification will occur or on terms that are acceptable to the Company.		The Company entered into a letter of intent dated June 24, 2020 to merge with B. Riley Principal Merger Corp. II (“BMRG II”). BMRG II is a special acquisition company (“SPAC”) incorporated for the purpose of effecting a merger, capital stock exchange, asset acquisition, stock purchase, reorganization or similar business combination with one or more businesses (the “SPAC transaction”). The SPAC transaction is currently expected to close in the fourth quarter of 2020 and would allow all holders of the Company’s equity and equity-linked securities to receive a combination of common stock of the continuing public company, which will be a wholly owned subsidiary of BMRG II. Accordingly, as part of the closing of the SPAC transaction, the Company currently expects substantially all the total amounts owed on the Company’s outstanding convertible notes will be converted into shares of the continuing public company. The merger would result in a net increase in cash to the Company of between approximately $66.4 million, assuming maximum shareholder redemptions permitted under the Business Combination Agreement, and $212.3 million, assuming minimum shareholder redemption, for which management plans to use to, among other things, fund the Company’s obligations as they become due. While management believes they will be able to close the SPAC transaction in October 2020, no assurance can be provided that such transaction will close or on terms that are acceptable to the Company. If the Company is unable to close the SPAC transaction, management plans to obtain additional outside capital to fund the Company’s current cost structure through the issuance of Series E Preferred shares and modify the terms of the Company’s outstanding convertible notes to, among other things, extend the current amounts owed to future periods. While management believes they would be able to issue Series E Preferred shares and modify the terms of the Company’s outstanding convertible notes in the event the SPAC transaction fails to close, no assurance can be provided that such issuance and modification will occur or on terms that are acceptable to the Company.
Impairment of long - lived assets								$ 1,590,000		1,441,000
Convertible notes payable related party								65,942,000		1,000,000
Fair value of convertible notes payable related party								76,559,000		$ 2,350,000
Fair value of the embedded derivative liability								$ 1,618,000
IPO [Member]
Summary of Significant Accounting Policies (Textual)
Sale of units	17,500,000
Class B Common Stock [Member]
Summary of Significant Accounting Policies (Textual)
Common stock, shares, issued		5,750,000	5,750,000	4,375,000		4,375,000		4,375,000
Common stock, shares, outstanding		5,750,000	5,750,000	4,375,000		4,375,000		4,375,000
Stock split		1 to 575
Purchase shares
Total members deficit			$ 575	$ 437		$ 437		$ 575	[1]		575		575			575
Class A Common Stock [Member]
Summary of Significant Accounting Policies (Textual)
Common stock, shares, issued				1,075,881		1,075,881
Common stock, shares, outstanding				1,075,881		1,075,881
Purchase shares				17,500,000		17,500,000	[1]
Total members deficit				$ 108	[1]	$ 108	[1]		[1]					[1]
Class A Common Stock [Member] | Private Placement [Member]
Summary of Significant Accounting Policies (Textual)
Purchase shares						9,075,000

[1] Includes an aggregate of 750,000 shares that are subject to forfeiture to the extent that the underwriter's over-allotment is not exercised in full (Note 4). On February 3, 2020, the Company conducted a 1:575 stock split and reclassification for each share outstanding (Note 4).

[2] Includes an aggregate of 656,250 shares that are subject to forfeiture to the extent that the underwriters over-allotment is not exercised in full (Note 4). On February 3, 2020, the Company conducted a 1:575 shares for each share outstanding (Note 4).