Exactly how much batteries could lower the cost of fuel cell-powered cars and SUVs would vary as car makers balanced the different strengths of fuel cells and batteries. Batteries and ultracapacitors can provide power at less cost than a fuel cell, but they run out of energy quickly. The strength of fuel cells is that they can keep running as long as they have hydrogen, and can be refueled faster than a battery can be recharged.

In the future, the mix of batteries and fuel cells could be optimized for different kinds of vehicles, says GM's Wicke. "There is a very broad mix of possibilities, starting with a fuel-cell vehicle which is augmented by a battery, all the way to a battery vehicle augmented by a fuel cell -- and you could have almost any mix in between," he says. GM is currently focused on the first approach, using a battery to boost the performance of a still relatively large fuel cell, while improving efficiency by capturing energy from braking.

While hybrid systems could help make fuel-cell vehicles more affordable, other obstacles need to be overcome before these vehicles take over the roads. Fuel cells can run only as long as hydrogen is available, and that will require better ways of storing hydrogen in the vehicle and distributing it. One of the reasons forklifts are a first application of hybrid fuel cells is that they never move far from their filling station.