X0202 4/A 2005-07-26 2005-07-28 0 0001103345 BEACON POWER CORP BCON 0001288003 PERSEUS 2000 EXPANSION LLC 2099 PENNSYLVANIA AVENUE NW SUITE 900 WASHINGTON DC 20006 1 0 1 0 Common Stock 2005-07-26 4 M 0 1785714 0.84 A 4642857 D Obligation to Purchase 0.84 2005-07-26 4 M 0 1 0.00 D 2005-04-22 2005-09-30 Common Stock 1785714 0 D Acquired pursuant to an Investment Agreement, dated as of April 22, 2005, by and among the Issuer, the Reporting Person and Perseus Capital, L.L.C., pursuant to which the Issuer had the right to require the Reporting Person to acquire shares of the Issuer's common stock on one or more dates to be specified in the future, at the Issuer's sole option. The Reporting Person has director representation and is deemed to be a director of the Issuer by deputization. By: Perseus 2000 Expansion, L.L.C. By: Rodd Macklin, Chief Financial Officer and Treasurer 2005-09-02