Exhibit 10.55

PROMISSORY NOTE

Principal	Loan Date	Maturity	Loan No	Call/Coll	Account	Officer	Initials
$1,000,000.00	09-15-2021	On Demand	11001	402 / 326	N9015196621	JXD9P
References in the boxes above are for Lender’s use only and do not limit the applicability of this document to any particular loan or item Any item above containing “**” has been omitted due to text length limitations.

Borrower:	Mechanical Technology, Incorporated 325 Washington Avenue Ext. Suite 3 Albany, NY  12205-5535	Lender:	KeyBank National Association NY62224F NY-KEY PLAZA CBB 66 S. Pearl Street Albany, NY  12207
Principal Amount: $1,000,000.00			Date of Note: September 15, 2021

PROMISE TO PAY. To repay Borrower’s loan, Mechanical Technology, Incorporated (“Borrower”) promises to pay to KeyBank National Association (“Lender”), or order, in lawful money of the United States of America, on demand, the principal amount of One Million & 00/100 Dollars (S1,000,000.00) or so much as may be outstanding, together with interest on the unpaid outstanding principal balance of each advance. Interest shall be calculated from the date of each advance until repayment of each advance.

PAYMENT. Borrower will pay this loan in full immediately upon Lender’s demand. Borrower will pay regular monthly payments of all accrued unpaid interest due as of each payment date, beginning October 1, 2021, with all subsequent interest payments to be due on the same day of each month after that. Unless otherwise agreed or required by applicable law, payments will be applied to first pay interest accrued to the day Lender receives the payment, then to bring principal current, then to pay any late fees, and then Lender will apply any remaining balance to reduce principal. Borrower will pay Lender at Lender’s address shown above or at such other place as Lender may designate in writing.

VARIABLE INTEREST RATE. The interest rate on this Note is subject to change from time to time based on changes in an index which is the Prime Rate announced by Lender (the “Index”). The Index is not necessarily the lowest rate charged by Lender on its loans and is set by Lender in its sole discretion. Lender will tell Borrower the current Index rate upon Borrower’s request. The interest rate change will not occur more often than each day that the Index changes. The interest rate will change automatically and correspondingly on the date of each announced change of the Index by Lender. Borrower understands that Lender may make loans based on other rates as well. The Index currently is 3.250% per annum. Interest on the unpaid principal balance of this Note will be calculated as described in the “INTEREST CALCULATION METHOD” paragraph using a rate of 0.750 percentage points over the Index (the “Margin”), adjusted if necessary for any minimum and maximum rate limitations described below, resulting in an initial rate of 4.000% per annum based on a year of 360 days. If Lender determines, in its sole discretion, that the Index has become unavailable or unreliable, either temporarily, indefinitely, or permanently, during the term of this Note, Lender may amend this Note by designating a substantially similar substitute index. Lender may also amend and adjust the Margin to accompany the substitute index. The change to the Margin may be a positive or negative value, or zero. In making these amendments, Lender may take into consideration any then-prevailing market convention for selecting a substitute index and margin for the specific Index that is unavailable or unreliable. Such an amendment to the terms of this Note will become effective and bind Borrower 10 business days after Lender gives written notice to Borrower without any action or consent of the Borrower. NOTICE: Under no circumstances will the interest rate on this Note be less than 3.000% per annum or more than the maximum rate allowed by applicable law.

PROMISSORY NOTE
(Continued)
Loan No. 11001	Page 2

INTEREST CALCULATION METHOD. Interest on this Note is computed on a 365/360 basis; that is, by applying the ratio of the interest rate over a year of 360 days, multiplied by the outstanding principal balance, multiplied by the actual number of days the principal balance is outstanding. All interest payable under this Note is computed using this method.

PREPAYMENT. Borrower agrees that all loan fees and other prepaid finance charges are earned fully as of the date of the loan and will not be subject to refund upon early payment (whether voluntary or as a result of default), except as otherwise required by law. Except for the foregoing, Borrower may pay without penalty all or a portion of the amount owed earlier than it is due. Early payments will not, unless agreed to by Lender in writing, relieve Borrower of Borrower’s obligation to continue to make payments of accrued unpaid interest. Rather, early payments will reduce the principal balance due. Borrower agrees not to send Lender payments marked “paid in full”, “without recourse”, or similar language. If Borrower sends such a payment, Lender may accept it without losing any of Lender’s rights under this Note, and Borrower will remain obligated to pay any further amount owed to Lender. All written communications concerning disputed amounts, including any check or other payment instrument that indicates that the payment constitutes “payment in full” of the amount owed or that is tendered with other conditions or limitations or as full satisfaction of a disputed amount must be mailed or delivered to: KeyBank National Association, NY62224F NY-KEY PLAZA CBB, 66 S. Pearl Street, Albany, NY 12207.

LATE CHARGE. If a regularly scheduled interest payment is 10 days or more late, Borrower will be charged 5.000% of the unpaid portion of the regularly scheduled payment or $25.00, whichever is greater. If Lender demands payment of this loan, and Borrower does not pay the loan in full within 10 days after Lender’s demand, Borrower also will be charged either 5.000% of the unpaid portion of the sum of the unpaid principal plus accrued unpaid interest or $25.00, whichever is greater.

INTEREST AFTER DEFAULT. Upon default, including failure to pay upon final maturity, the interest rate on this Note shall be increased by adding an additional 3.000 percentage point margin (“Default Rate Margin”). The Default Rate Margin shall also apply to each succeeding interest rate change that would have applied had there been no default. However, in no event will the interest rate exceed the maximum interest rate limitations under applicable law.

PROMISSORY NOTE
(Continued)
Loan No. 11001	Page 3

LENDER’S RIGHTS. Upon Lender’s demand, Lender may declare the entire unpaid principal balance under this Note and all accrued unpaid interest immediately due, and then Borrower will pay that amount.

ATTORNEYS’ FEES; EXPENSES. Borrower agrees to pay all costs and expenses Lender incurs to collect this Note. This includes, subject to any limits under applicable law, Lender’s reasonable attorneys’ fees and Lender’s legal expenses whether or not there is a lawsuit, including reasonable attorneys’ fees and expenses for bankruptcy proceedings (including efforts to modify or vacate any automatic stay or injunction), and appeals. If not prohibited by applicable law, Borrower also will pay any court costs, in addition to all other sums provided by law.

JURY WAIVER. Lender and Borrower hereby waive the right to any jury trial in any action, proceeding, or counterclaim brought by either Lender or Borrower against the other.

GOVERNING LAW. This Note will be governed by federal law applicable to Lender and, to the extent not preempted by federal law, the laws of the State of New York without regard to its conflicts of law provisions. This Note has been accepted by Lender in the State of New York.

DISHONORED ITEM FEE. Borrower will pay a fee to Lender of $20.00 if Borrower makes a payment on Borrower’s loan and the check or preauthorized charge with which Borrower pays is later dishonored.

RIGHT OF SETOFF. To the extent permitted by applicable law, Lender reserves a right of setoff in all Borrower’s accounts with Lender (whether checking, savings, or some other account and whether evidenced by a certificate of deposit). This includes all accounts Borrower holds jointly with someone else and all accounts Borrower may open in the future. However, this does not include any IRA or Keogh accounts, or any trust accounts for which setoff would be prohibited by law. Borrower authorizes Lender, to the extent permitted by applicable law, to charge or setoff all sums owing on the indebtedness against any and all such accounts.

LINE OF CREDIT. This Note evidences a revolving line of credit. Advances under this Note may be requested either orally or in writing by Borrower or as provided in this paragraph. Lender may, but need not, require that all oral requests be confirmed in writing. All communications, instructions, or directions by telephone or otherwise to Lender are to be directed to Lender’s office shown above. Borrower agrees to be liable for all sums either: (A) advanced in accordance with the instructions of an authorized person or (B) credited to any of Borrower’s accounts with Lender. The unpaid principal balance owing on this Note at any time may be evidenced by endorsements on this Note or by Lender’s internal records, including daily computer print-outs.

ANNUAL ADMINISTRATIVE FEE. Borrower will pay an annual administrative fee of $1,000.00 on the date of the Note and $1,000.00 on each subsequent anniversary date of the Note. This fee does not constitute the commitment of Lender to make advances under the Note.

PROMISSORY NOTE
(Continued)
Loan No. 11001	Page 4

DEMAND LINE OF CREDIT. Borrower understands that Lender is authorized to make an annual (or more frequent) credit review based upon Borrower’s current financial condition in determining whether to continue the line of credit. Nevertheless, Lender may, at any time, with or without cause, refuse to advance funds or extend credit under the line of credit.

AUTHORIZATION TO CHARGE DEPOSIT ACCOUNT FOR LOAN PAYMENTS. Borrower hereby authorizes Lender automatically to deduct from Borrower’s designated deposit account (“Account”), payments due on the loan on the date each payment is due.

Borrower authorizes Lender to deduct amounts subject to change without prior notification to Borrower of the new amount to be deducted due to: (1) late charges assessed; (2) delinquent amounts due or (3) any other payment amount required under the terms of the loan. If the funds in the Account are insufficient to cover any payment, Lender shall not be obligated to advance funds to cover the payment. Lender shall not be liable for dishonoring checks or other items due to insufficient funds caused by the honoring of this Authorization.

Borrower may terminate this authorization by giving not less than three (3) days prior written notice to the Loan Services Department. This authorization may be terminated at any time by Lender.

SUCCESSOR INTERESTS. The terms of this Note shall be binding upon Borrower, and upon Borrower’s heirs, personal representatives, successors and assigns, and shall inure to the benefit of Lender and its successors and assigns.

GENERAL PROVISIONS. If any part of this Note cannot be enforced, this fact will not affect the rest of the Note. Lender may delay or forgo enforcing any of its rights or remedies under this Note without losing them. Borrower and any other person who signs, guarantees or endorses this Note, to the extent allowed by law, waive presentment, demand for payment, and notice of dishonor. Upon any change in the terms of this Note, and unless otherwise expressly stated in writing, no party who signs this Note, whether as maker, guarantor, accommodation maker or endorser, shall be released from liability. All such parties agree that Lender may renew or extend (repeatedly and for any length of time) this loan or release any party or guarantor or collateral; or impair, fail to realize upon or perfect Lender’s security interest in the collateral; and take any other action deemed necessary by Lender without the consent of or notice to anyone. All such parties also agree that Lender may modify this loan without the consent of or notice to anyone other than the party with whom the modification is made. The obligations under this Note are joint and several.

PRIOR TO SIGNING THIS NOTE, BORROWER READ AND UNDERSTOOD ALL THE PROVISIONS OF THIS NOTE, INCLUDING THE VARIABLE INTEREST RATE PROVISIONS. BORROWER AGREES TO THE TERMS OF THE NOTE.

PROMISSORY NOTE
(Continued)
Loan No. 11001	Page 5

BORROWER ACKNOWLEDGES RECEIPT OF A COMPLETED COPY OF THIS PROMISSORY NOTE.

BORROWER:

MECHANICAL TECHNOLOGY, INCORPORATED

By:	/s/ Jessica Thomas
	Jessica Thomas, CFO of Mechanical Technology, Incorporate