X0202 4/A 2005-04-22 2005-05-26 0 0001103345 BEACON POWER CORP BCON 0001090098 PERSEUS CAPITAL LLC 2099 PENNSYLVANIA AVENUE, NW SUITE 900 WASHINGTON DC 20006 1 0 1 0 Warrant 2.25 2005-04-22 4 A 0 1333333 100000.00 A 2005-04-22 2007-05-23 Common Stock 1333333 1333333 D This disclosure item references a Warrant, initially dated May 23, 2000, exercisable for 1,333,333 shares of the Issuer's common stock. Pursuant to an Investment Agreement among the Issuer, the Reporting Person and Perseus 2000 Expansion, L.L.C., dated as of April 22, 2005 and previously disclosed to and filed with the Securities Ecxhange Commission, the Reporting Person agreed to pay to the Issuer $100,000 in exchange for an extension of the expiration of the date of the Warrant from May 23, 2005 to May 23, 2007. The payment for this extension was made on May 24, 2005. The Reporting Person has director representation and is deemed to be a director of the Issuer by deputization. By: Perseus Capital, L.L.C. By: Rodd Macklin, Chief Financial Officer and Treasurer 2005-09-02