A battery system for an electric vehicle should be designed and developed in concert with the other components of the propulsion system. Technology development efforts sponsored by the U.S. Department of Energy are addressing all the constituent electric vehicle component technologies, including the battery subsystem technologies, from the perspective of the complete propulsion system. This approach is considered to be essential for three reasons. First, the ultimate viability of a given battery technology can only be assured in the context of a complete propulsion system. Second, many required battery subsystem technology advancements can only be addressed in concert with the other propulsion system components. Third, development and testing of battery subsystem technologies in conjunction with powertrain subsystem technology development is necessary in order to provide essential information to the battery developer and to the vehicle developer that can not be obtained when battery development is performed as a discrete activity.