Exploratory studies on small plastic lithium-ion battery test cells with improved cathode material show high pulse power capability and outstanding stability both in a 25 degreesC pulse cycling test and in a 55 degreesC calendar life test. Typical discharge pulse power values are 60 mW/cm(2). After 50,000 pulse cycles at 5 C rates, cells at 25 degreesC retain 100% of their initial 1 C capacity and 75% of their pulse power capability. After 60 days at 55 degreesC, cells measured at 25 degreesC retain 98% of their initial 1 C capacity and 70% of their pulse power capability. This performance is an excellent basis for the development of long life batteries for hybrid vehicles, as shown by a calculated scale up to a 30 kW hybrid battery for a "Fast Response Engine".