The switch from hybrid to plug-in hybrid doesn't come cheap, though. The battery and installation costs $9,995, plus an extra $400 "destination fee" and taxes.
The battery, called Hymotion 5, is designed to fit into the spare tire slot underneath the trunk of Prius model years 2004 to 2008. The company didn't say when the batteries would be available.
A123 Systems said the extended-life battery has been tested over 200,000 miles of "real life" conditions and that it should not void Toyota's warranty unless it's directly responsible for a failure.
There are a number of converted plug-in hybrids, but they are not yet manufactured from automakers. Last year, A123 Systems bought Hymotion, which has a network of installers who are expert in plug-in hybrids.
With a plug-in hybrid, a person can boost gas efficiency from about 40 miles per gallon in a Prius to more than 100 miles per gallon depending on what kind of driving you do. If there is a lot of stop and go driving for trips under about 30 miles, the braking system can recharge the battery and substantially cut down on gas use.
The Web site underscores the large interest in plug-in hybrid cars for purely environmental reasons, rather than.
Rather than calculate the return on investment, the site allows consumers to calculate what sort of gas mileage they can expect and how it will affect their carbon footprint.
Although there are not any production plug-in hybrids, Toyota and General Motors are expected to release their own versions.
GM, in fact, has signed up for a partnership with A123 Systems to use its lithium ion battery with thethat can run on different liquid fuels.