X0306 4 2012-09-07 0 0001167178 A123 SYSTEMS, INC. AONE 0001472755 McCarthy Jeffrey P C/O A123 SYSTEMS, INC. 200 WEST STREET WALTHAM MA 02451 1 0 0 0 Common Stock, $0.001 par value 10000 D Common Stock, $0.001 par value 2012-09-07 4 S 0 557768 0.1979 D 398677 I By North Bridge Venture Partners IV-A, L.P. Common Stock, $0.001 par value 2012-09-07 4 S 0 264772 0.1979 D 189249 I By North Bridge Venture Partners IV-B, L.P. Common Stock, $0.001 par value 2012-09-07 4 S 0 790072 0.1979 D 564721 I By North Bridge Venture Partners V-A, L.P. Common Stock, $0.001 par value 2012-09-07 4 S 0 387388 0.1979 D 276897 I By North Bridge Venture Partners V-B, L.P. Common Stock, $0.001 par value 2012-09-10 4 S 0 398677 0.2199 D 0 I By North Bridge Venture Partners IV-A, L.P. Common Stock, $0.001 par value 2012-09-10 4 S 0 189249 0.2199 D 0 I By North Bridge Venture Partners IV-B, L.P. Common Stock, $0.001 par value 2012-09-10 4 S 0 564721 0.2199 D 0 I By North Bridge Venture Partners V-A, L.P. Common Stock, $0.001 par value 2012-09-10 4 S 0 276897 0.2199 D 0 I By North Bridge Venture Partners V-B, L.P. Includes 7,500 restricted stock units ("RSUs"). Upon vesting thereof, the Reporting Person is entitled to receive one (1) share of common stock for each one (1) RSU. The transaction was executed in multiple trades in prices ranging from $0.1950 to $0.2129, inclusive. The price reported in Column 4 above reflects the weighted average sale price. The Reporting Person hereby undertakes to provide upon request to the SEC staff, the Issuer, or a stockholder of the Issuer, information regarding the number of shares and prices at which the transaction was effected. The Reporting Person disclaims beneficial ownership of these shares except to the extent of his pecuniary interest therein, and the inclusion of these shares in this report shall not be deemed an admission of beneficial ownership of all of the reported shares for purposes of Section 16 or for any other purpose. The transaction was executed in multiple trades in prices ranging from $0.2000 to $0.5150, inclusive. The price reported in Column 4 above reflects the weighted average sale price. The Reporting Person hereby undertakes to provide upon request to the SEC staff, the Issuer, or a stockholder of the Issuer, information regarding the number of shares and prices at which the transaction was effected. /s/ Kenneth J. DiPoto, as Attorney-in-Fact for Jeffrey P. McCarthy 2012-09-11