Ok I’ll tell you up front this isn’t cheap…how about 10k, so the person who is buying it - is doing so for the planet and not for the pocketbook savings.

CNet has the story about a123Systems that sells the upgrade.

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.

For the average driver that would mean going to the gas station 5 times a year…remember though…it’s 10,000 dollars.