Their batteries are also expensive and heavy - they often double the weight and cost of the car. And they need replacement every two or three years. Cars that use both a gasoline engine and an electric motor to save fuel and reduce emissions. Hybrids run on gasoline, diesel, compressed natural gas, ethanol, or some other combustible fuel. They also use a small bank of batteries that cost and weigh less than those in pure electric cars.
Hybrids also use a much smaller gasoline engine than conventional cars use for better economy.
Early hybrids worked like electric cars, using an electric motor to power the wheels. The gas engine served only as a generator to keep the batteries charged. But most modern hybrids, including the Toyota Prius, use a parallel configuration that alternately uses an electric motor and batteries, a gasoline engine, or both to drive the wheels. This allows both the electric motor and the gasoline engine to do what they do best. Gasoline engines excel at traveling long distances at highway speeds.