X0202 4 2005-08-25 0 0001103345 BEACON POWER CORP BCON 0000927752 PEARL FRANK H C/O PERSEUS CAPITAL, L.L.C. 2099 PENNSYLVANIA AVENUE, NW, SUITE 900 WASHINGTON DC 20006 0 0 1 0 Common Stock 2005-08-25 4 S 0 332549 4.5885 D 8145208 I Through Perseus Capital, L.L.C. and Perseus 2000 Expansion, L.L.C. The Reporting Person is a member of Perseus Investors Group, L.L.C., which, as previously reported, acquired the reported securities from Perseus Capital, L.L.C., of which Perseus Investors Group, L.L.C. is a member, as part of pro rata distribution to its members based on capital percentages. The Reporting Person is the Chairman of Perseus, L.L.C., which through certain subsidiary entities controls Perseus Capital, L.L.C. and Perseus 2000 Expansion, L.L.C., which severally beneficially own the reported securities. The Reporting Person disclaims beneficial ownership of the reported securities, except to the extent of his pecuniary interest therein. By: Rodd J. Macklin, Attorney-in-Fact 2005-08-30