What type of battery cells did Tesla use in the original Roadster?

The original Tesla Roadster used lithium-ion battery cells.

Tesla’s first production car employed thousands of small cylindrical lithium-ion cells arranged into a larger battery pack. This approach differed from the large custom-format battery modules used by many earlier electric vehicles. Lithium-ion chemistry offered a useful combination of energy density, power capability, and rechargeable-cycle performance.

The Roadster’s battery system was one of the vehicle’s most important innovations. Tesla developed monitoring and safety systems to manage the many individual cells, including temperature control and electronic battery management. The pack stored enough energy to give the lightweight sports car a much longer range than many contemporary electric vehicles.

The answer is sometimes confused with nickel-metal hydride, a battery chemistry used in several earlier hybrid vehicles. The Roadster was not powered by an alkaline or lead-acid traction battery.