UNITED STATES	
SECURITIES AND EXCHANGE COMMISSION	
Washington, D.C.  20549	

SCHEDULE 13G*	
(Rule 13d-102)	
 	
INFORMATION TO BE INCLUDED IN STATEMENTS FILED PURSUANT	
TO RULES 13d-1(b), (c), AND (d) AND AMENDMENTS THERETO FILED	
PURSUANT TO RULE 13d-2	
(Amendment No. 3 )*	

 	Active Power, Inc.	 	
(Name of Issuer)	
 	
 	Common Stock, par value $0.001	 	
(Title of Class of Securities)	

 	00504W100	 	
(CUSIP Number)	

 	December 31, 2011	 	
(Date of Event Which Requires Filing of the Statement)	

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

£ Rule 13d-1(b)
S Rule 13d-1(c)
 
£ Rule 13d-1(d)
 
*The remainder of this cover page shall be filled out for a reporting person’s initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter the disclosures provided in a prior cover page.
The information required on the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the Securities Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however,  see  the  Notes ).
Page 1 of 9	

 	 	

CUSIP No. 00504W100	13G	Page 2 of 9 Pages	
  
1	NAME OF REPORTING PERSONS
 
Kinderhook Partners, L.P.
 	
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (see instructions)
(a)   ¨
(b)   x
 	
3	SEC USE ONLY
 	
4	CITIZENSHIP OR PLACE OF ORGANIZATION
 
         Delaware	

NUMBER OF	5	SOLE VOTING POWER
 
0	
SHARES
BENEFICIALLY
OWNED BY	6	SHARED VOTING POWER
 
8,809,456	
EACH
REPORTING
PERSON	7	SOLE DISPOSITIVE POWER
 
0	
WITH
 	8	SHARED DISPOSITIVE POWER
 
8,809,456	

9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
 
         8,809,456	
10	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES
¨	
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)
 
         11.0%	
12	TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)
 
        PN	
  
Page 2 of 9	

 	 	
 
CUSIP No. 00504W100	13G	Page 3 of 9 Pages	
  
1	NAME OF REPORTING PERSONS
 
Kinderhook GP, LLC
 	
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (see instructions)
(a)   ¨
(b)   x
 	
3	SEC USE ONLY
 	
4	CITIZENSHIP OR PLACE OF ORGANIZATION
 
         Delaware	

NUMBER OF	5	SOLE VOTING POWER
 
0	
SHARES
BENEFICIALLY
OWNED BY	6	SHARED VOTING POWER
 
8,809,456	
EACH
REPORTING
PERSON	7	SOLE DISPOSITIVE POWER
 
0	
WITH
 	8	SHARED DISPOSITIVE POWER
 
8,809,456	

9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
 
         8,809,456	
10	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES
¨	
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)
 
         11.0%	
12	TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)
 
        OO	
 
Page 3 of 9	

 	 	
 
CUSIP No. 00504W100	13G	Page 4 of 9 Pages	
  
1	NAME OF REPORTING PERSONS
 
Stephen J. Clearman
 	
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (see instructions)
(a)   ¨
(b)   x
 	
3	SEC USE ONLY
 	
4	CITIZENSHIP OR PLACE OF ORGANIZATION
 
         Delaware	

NUMBER OF	5	SOLE VOTING POWER
 
0	
SHARES
BENEFICIALLY
OWNED BY	6	SHARED VOTING POWER
 
8,809,456	
EACH
REPORTING
PERSON	7	SOLE DISPOSITIVE POWER
 
0	
WITH
 	8	SHARED DISPOSITIVE POWER
 
8,809,456	

9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
 
         8,809,456	
10	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES
¨	
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)
 
         11.0%	
12	TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)
 
        IN	
 
Page 4 of 9	

 	 	
  
CUSIP No. 00504W100	13G	Page 5 of 9 Pages	
  
1	NAME OF REPORTING PERSONS
 
Tushar Shah
 	
2	CHECK THE APPROPRIATE BOX IF A MEMBER OF A GROUP (see instructions)
(a)   ¨
(b)   x
 	
3	SEC USE ONLY
 	
4	CITIZENSHIP OR PLACE OF ORGANIZATION
 
         Delaware	

NUMBER OF	5	SOLE VOTING POWER
 
0	
SHARES
BENEFICIALLY
OWNED BY	6	SHARED VOTING POWER
 
8,809,456	
EACH
REPORTING
PERSON	7	SOLE DISPOSITIVE POWER
 
0	
WITH
 	8	SHARED DISPOSITIVE POWER
 
8,809,456	

9	AGGREGATE AMOUNT BENEFICIALLY OWNED BY EACH REPORTING PERSON
 
         8,809,456	
10	CHECK BOX IF THE AGGREGATE AMOUNT IN ROW (9) EXCLUDES CERTAIN SHARES
¨	
11	PERCENT OF CLASS REPRESENTED BY AMOUNT IN ROW (9)
 
         11.0%	
12	TYPE OF REPORTING PERSON (SEE INSTRUCTIONS)
 
        IN	
 
Page 5 of 9	

 	 	
 
CUSIP No. 00504W100	13G	Page 6 of 9 Pages	

 	Item 1(a).	Name of Issuer: Active Power, Inc. (the “Issuer”)	

 	Item 1(b).	Address of Issuer’s Principal Executive Offices:	
 
2128 W. Braker Lane, BK12
Austin, TX 78758
 	Item 2(a).	Name of Person Filing:	
 
Kinderhook Partners, LP
Kinderhook GP, LLC
Stephen J. Clearman
Tushar Shah
 
 	Item 2(b).	Address of Principal Business Office or, if none, Residence:	
 
1 Executive Drive, Suite 160
Fort Lee, New Jersey 07024
 	Item 2(c).	Citizenship:	
 
Kinderhook Partners, LP - Delaware
Kinderhook GP, LLC - Delaware
Stephen J. Clearman - United States of America
Tushar Shah - United States of America 
 	Item 2(d).	Title of Class of Securities: Common Stock, par value $0.001	

 	Item 2(e).	CUSIP Number: 00504W100	

 	Item 3.	If this statement is filed pursuant to Rules 13d-1(b), or 13d-2(b) or (c), check whether the person filing is a:	
 	
(a)	[__]	Broker or dealer registered under Section 15 of the Act (15 U.S.C 78o);
(b)	[__]	Bank as defined in Section 3(a)(6) of the Act (15 U.S.C 78c);
(c)	[__]	Insurance company as defined in Section 3(a)(19) of the Act (15 U.S.C 78c);
(d)	[__]	Investment company registered under Section 8 of the Investment Company Act of 1940 (15 U.S.C. 80a-8);
(e)	[__]	An investment adviser in accordance with Rule 13d-1(b)(1)(ii)(E);
(f)	 [__]	An employee benefit plan or endowment fund in accordance with § 240.13d-1(b)(1)(ii)(F);
(g)	[__]	A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G);
(h)	[__]	A savings association as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);
Page 6 of 9	

 	 	

CUSIP No. 00504W100	13G	Page 7 of 9 Pages	
 (i)	 [__]	A church plan that is excluded from the definition of an investment company under Section 3(c)(14) of the Investment Company Act (15 U.S.C. 80a-3);
(j)	 [__]	A non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J);
(k)	[__]	Group, in accordance with § 240.13d-1(b)(1)(ii)(K).
If filing as a non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J), please specify the type of institution: _________________ 
This statement is filed pursuant to Rule 13d-1(c).
 
 	Item 4.	Ownership:	
 
Provide the following information regarding the aggregate number and percentage of class of securities of the issuer identified in Item 1.
(a)	Amount beneficially owned:
(b)	Percent of Class:	
(c)	Number of shares as to which such person has:
 	(i)	sole power to vote or to direct the vote	
  
 	(ii)	shared power to vote or to direct the vote:	

 	(iii)	sole power to dispose or to direct the disposition of:	

 	(iv)	shared power to dispose or to direct the disposition of:	
Ownership as of December 31, 2011 is incorporated herein by reference from items (5) - (9) and (11) of the cover page of this Schedule 13G.
 
 	Item 5.	Ownership of Five Percent or Less of a Class:	
 
If this statement is being filed to report the fact that as of the date hereof the reporting person has ceased to be the beneficial owner of more than 5 percent of the class of securities, check the following [ _ ].
 
 	Item 6.	Ownership of More than Five Percent on Behalf of Another Person:	
  
Kinderhook Partners, L.P. specifically disclaims beneficial ownership in the shares of Common Stock reported herein except to the extent of its pecuniary interest therein, if any.
 
Kinderhook GP, LLC specifically disclaims beneficial ownership in the shares of Common Stock reported herein except to the extent of its pecuniary interest therein, if any .
 
Page 7 of 9	

 	 	

CUSIP No. 00504W100	13G	Page 8 of 9 Pages	
 
Mr. Stephen J. Clearman and Mr. Tushar Shah are co-managing members of Kinderhook GP, LLC, the General Partner of Kinderhook Partners, L.P., and as a result, Mr. Clearman and Mr. Shah may be deemed to control such entities. In addition, Mr. Clearman and Mr. Shah are co-managing members of Kinderhook Capital Management, LLC, the Investment Adviser of Kinderhook Partners, L.P., responsible for making investment decisions with respect to the Partnership. Accordingly, Mr. Clearman and Mr. Shah may be deemed to have a beneficial interest in the shares of Common Stock by virtue of their indirect control of the Partnership’s, General Partner’s, and Investment Adviser’s power to vote and/or dispose of the shares of Common Stock. Mr. Clearman and Mr. Shah disclaim beneficial ownership of the shares of Common Stock except to the extent of their pecuniary interest, if any, therein.
 
 	Item 7.	Identification and Classification of the Subsidiary which Acquired the Security Being Reported on by the Parent Holding Company or Control Person:	
 
Not Applicable
 
 	Item 8.	Identification and Classification of Members of the Group:	
 
Not Applicable
  
 	Item 9.	Notice of Dissolution of Group:	
 
Not Applicable
 
 	Item 10.	Certifications:	
   
SIGNATURE
After reasonable inquiry and to the best of its knowledge and belief, I certify (the undersigned certifies) that the information set forth in this statement is true, complete and correct.
 	2/13/2011	
 	(Date)	
 	 	
 	/s/ Tushar Shah	
 	(Signature)	
 	 	
 	Tushar Shah	
 	Name and Title	
 
 	2/13/2011	
 	(Date)	
 	 	
 	/s/ Stephen J. Clearman	
 	(Signature)	
 	 	
 	Stephen J. Clearman	
 	Name and Title	
 
Page 8 of 9	

 	 	

CUSIP No. 00504W100	13G	Page 9 of 9 Pages	
 
 	2/13/2011	
 	(Date)	
 	 	
 	/s/ Tushar Shah	
 	(Signature)	
 	 	
 	Tushar Shah - Managing Member of Kinderhook GP, LLC	
 	Name and Title	
 
 	2/13/2011	
 	(Date)	
 	 	
 	/s/ Tushar Shah	
 	(Signature)	
 	 	
 	Tushar Shah - Managing Member of Kinderhook Partners, LP	
 	Name and Title	
 
Page 9 of 9