Electro Energy Inc. is developing a prototype battery pack-–a custom version of its bipolar nickel metal hydride battery-–for the California Cars Initiative (CalCars) Toyota PRIUS+ test vehicle. The project retrofits the Prius with a high-energy content battery that becomes the vehicle's primary power source for local travel, eliminating the use of gasoline for short trips. For longer trips, the car can revert to conventional hybrid operation, which uses a combination of gasoline and battery power. The battery can be recharged at off-peak hours, further supporting energy conservation.

Ron Gremban, the lead technologist on CalCars' PRIUS+ project, said Electro Energy's prototype pack has lower internal resistance than the Prius' original hybrid battery, resulting in higher power availability and lower energy losses. It is expected to improve average typical mixed-driving gasoline consumption and range performance to 90 mpg plus electricity for the first 40 to 50 miles after each charge, without compromising the Prius' original performance of 45 mpg."