A battery system for a vehicle capable of being driven by electric power is disclosed. The vehicle includes at least one motor/generator and a battery system for supplying electrical power to and receiving electrical power from the motor/generator. The battery system includes multiple battery packs, each comprising a plurality of cells. The plurality of cells in each battery pack are electrically connected with one another. Multiple battery pack housings are provided to house the plurality of cells. Each battery pack housing facilitates electrical connection to one or more other battery pack. The system also includes a compartment containing the multiple battery packs in their housings. The compartment facilitates electrical connection to the motor/generator.