The battery pack in the Tesla Roadster is the result of innovative systems engineering and 20 years of advances in Lithium-ion cell technology. Tesla's ingenious battery pack architecture enables world-class acceleration, safety, range, and reliability. The non-toxic pack is built at Tesla’s Headquarters in Northern California.

The pack weighs 990 pounds, stores 56 kWh of electric energy, and delivers up to 215 kW of electric power. Tesla battery packs have the highest energy density in the industry. To achieve this energy density, Tesla starts with thousands of best-in-class Lithium-ion cells and assembles them into a liquid-cooled battery pack, wrapped in a strong metal enclosure. The battery is optimized for performance, safety, longevity, and cost.

http://www.teslamotors.com/roadster/technology/battery