Ultracapacitors offer a way to extend the life of a hybrid vehicle's power source, reducing the need to oversize its battery packs. Unlike batteries, ultracapacitors don't rely on chemical reactions to store energy, and they don't degrade significantly over the life of a car, even when they are charged and discharged in very intense bursts that can damage batteries. The drawback is that they store much less energy than batteries--typically, an order of magnitude less. If, however, ultracapacitors were paired with batteries, they could protect batteries from intense bursts of power, Bohn says, such as those needed for acceleration, thereby extending the life of the batteries. Ultracapacitors could also ensure that the car can accelerate just as well at the end of its life as at the beginning.