A fuel cell vehicle (FCV) is an electric vehicle that uses a fuel cell rather than a battery to provide electricity that powers motors at the wheels. While a battery must be recharged after all its fuel has reacted; a fuel cell is a "refillable battery"—filling the fuel tank recharges the vehicle. The fuel cell onboard the vehicle produces electricity directly from the reaction of hydrogen and oxygen. FCVs can be twice as efficient as similarly sized conventional vehicles. They can also be equipped with other advanced technologies to increase efficiency, such regenerative braking systems that capture the energy lost during braking and store it in an upsized battery.