Toyota executives cited two reasons for their choice of nickel-metal hydride.
"Its a tried-and-true technology that has a decade of success behind it," Toyota spokesman Greg Thome told us. "It's also got the lower-cost technology that we can offer to younger hybrid adopters." The nickel-metal hydride battery pack is located under the rear passenger seat, near the center of the vehicle, and sits low in the chassis to lower the vehicle's center of gravity.
Toyota engineers also made an effort to optimize the motor-generator for the five-door subcompact, Thome said.
"In addition to making the battery smaller, we took special pains to keep the motor-generator smaller, as well," he said. "It's constructed the same as the Prius Liftback's motor-generator, but we tried to optimize the sizing and packaging for a smaller vehicle." The motor's output is 60hp, versus 80hp on earlier Priuses.
The Prius family, unveiled two years ago at the Detroit Auto Show, also includes the Prius Liftback, the Prius v, and the plug-in Prius PHV, which will be introduced this year.