Execution Version

A123 SYSTEMS, INC.

SIXTH AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

This Agreement dated as of May 6, 2008 is entered into by and among A123 Systems, Inc., a Delaware corporation (the "Company"), Ricardo Fulop, Gilbert Riley, Jr. and Yet-Ming Chiang (individually, a "Founder" and collectively, the "Founders"), the Massachusetts Institute of Technology ("M.I.T."), Comerica Bank ("Comerica"), Heller Financial Leasing, Inc. ("Heller"), Silicon Valley Bank ("SVB"), Gold Hill Venture Lending 03, L.P. ("Gold Hill"), the individuals and entities listed as Series A Purchasers on Exhibit A hereto (the "Series A Purchasers"), the individuals and entities listed as Series A-1 Purchasers on Exhibit A hereto (the "Series A-1 Purchasers"), the individuals and entities listed as Series B Purchasers on Exhibit A hereto (the "Series B Purchasers"), the individuals and entities listed as Series C Purchasers on Exhibit A hereto (the "Series C Purchasers"), the individuals and entities listed as Series D Purchasers on Exhibit A hereto (the "Series D Purchasers") and the individuals and entities listed as Series E Purchasers on Exhibit A hereto (the "Series E Purchasers"). The Series A Purchasers, Series A-1 Purchasers, Series B Purchasers, Series C Purchasers, Series D Purchasers, Series E Purchasers, SVB and Gold Hill are collectively referred to herein as the "Investors". The term "Investors" shall include (i) M.I.T. only with respect to its rights and obligations relating to the shares of Series A Preferred, Series B Preferred, Series C Preferred and Series D Preferred (each as defined below) held by M.I.T and (ii) Gold Hill only with respect to its rights and obligations relating to the shares of Series C Preferred and Series D Preferred held by Gold Hill. The term "M.I.T." shall not include any transferees of M.I.T.

Recitals

WHEREAS, on December 4, 2001, the Company and M.I.T. entered into an Exclusive Patent License Agreement (the "License Agreement");

WHEREAS, the Series A Purchasers acquired an aggregate of 8,300,000 shares of Series A Convertible Preferred Stock of the Company ("Series A Preferred") pursuant to the terms of a Series A Convertible Preferred Stock Purchase Agreement dated as of December 17, 2001, by and among the Company and the Series A Purchasers (the "Series A Purchase Agreement");

WHEREAS, on July 19, 2002, the Company issued to Comerica a warrant to purchase up to an aggregate of 22,500 shares of Series A Preferred;

WHEREAS, the Series A-1 Purchasers acquired an aggregate of 2,925,000 shares of Series A-1 Convertible Preferred Stock of the Company (the "Series A-1 Preferred") pursuant to the terms of a Series A-1 Convertible Preferred Stock Purchase Agreement dated as of November 25, 2002 by and among the Company and the Series A-1 Purchasers (the "Series A-1 Purchase Agreement");

WHEREAS, the Series B Investors acquired an aggregate of 9,623,750 shares of Series B Convertible Preferred Stock of the Company (the "Series B Preferred") pursuant to the terms of a Series B Convertible Preferred Stock Purchase Agreement dated as of June 1, 2004 by and among the Company and the Series B Purchasers (the "Series B Purchase Agreement");

WHEREAS, on February 24, 2005, the Company issued to Heller a warrant to purchase up to an aggregate of 67,366 shares of Series B Preferred;

WHEREAS, the Series C Purchasers acquired an aggregate of 8,899,395 shares of Series C Convertible Preferred Stock of the Company (the "Series C Preferred") pursuant to the terms of a Series C Convertible Preferred Stock Purchase Agreement dated as of January 30, 2006 by and among the Company and the Series C Purchasers (the "Series C Purchase Agreement");

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