'Green' energy companies in Mass.
Went public: 2009
Employees: 2,000 employees worldwide
Revenue/investment: $97.3 million in revenue in 2010
What it does: A123 makes powerful and quick-charging batteries using lithium-ion technology. The company has partnership agreements with several car companies that are interested in using the technology for electric vehicles. The company also supplies its lithium-ion battery technology for use in the electric power grid.