Fuel cells are different than batteries, because instead of storing energy they are used as electrochemical conversion devices. The chemicals used for conversion by fuel cells are hydrogen and oxygen which are then turned into water and in this process electricity is produced. This electrical energy is then used to power a car. As long as the chemicals constantly are added and flow into the system, the fuel cell never dies and that is just one way that they contribute to environmentally friendly motoring.
Some types of fuel cells are more efficient than others, and fortunately one of the most promising kinds to be used in the future for cars, is one of the most efficient. The hydrogen fuel cell works at about 50% efficiency and that means that half of the hydrogen added will be converted to electrical energy. The other half is released as heat and neither of those products damages the environment. Cars that will use hydrogen fuel cells in the future will have no negative impact on the environment and therefore can be driven without feeling guilty.
Cars that use fuel cells also do not deplete any of our limited resources, such as oil. There is plenty of hydrogen available to make fuel with, but the process to extract hydrogen is not yet refined enough that it will be a low cost alternative. However, hydrogen is sustainable and available and that saves our environment from future drilling to find more oil. Hydrogen also burns cleanly and cars that use fuel cells have zero emissions, therefore releasing no pollutants.