How do you get them to last? How do you deal with extending the range? How can you accelerate and decelerate without using too much energy? To answer to these and other gripes, AFS Trinity Power, a company based in Washington state, presents the Extreme Hybrid Storage System.
The system combines a typical battery with a device called an ultra-capacitor. Batteries store lots of energy but are slow to deliver it. Capacitors, on the other hand, can release great amounts of power very quickly. The capacitor easily handles changes in acceleration, placing less stress on the battery and extending its life.
Source: http://green.blogs.nytimes.com/2010/07/26/for-hybrid-cars-a-hybrid-invention/
http://afstrinity.com/press/articles/AFST-SystemCost-05Aug2010.pdf