In the first quarter of 2008, A123 Systems and Hymotion plan to market a $9500 USD add-on for the Toyota Prius. This cost, which includes installation, is expected to increase your Prius’ fuel economy to 150 MPG in the city. Pretty dang impressive! If it works reliably and safely: I do have some minor qualms about installing a massive lithium ion battery in my car. I’m not saying the “massive lithium battery in the trunk” idea is completely bad… I just don’t want to Beta test or even production test that.
Also, please be aware that this fuel economy increase incurs the additional cost of electricity to recharge this battery. That’s right, when you park your Prius you will need to plug your car into an electrical extension cord to recharge this additional battery.