The purpose of the battery is to store electrical energy. It does this by converting the electrical energy supplied to it into chemical energy so that when an electrical current is required the energy change is reverse.Lead–acid batteries are able to supply high surge current, which means that the cells maintain a relatively large power-to-weight ratio. This feature, along with their low cost, makes lead–acid batteries attractive for use in motor vehicles. Nickel-hydrogen batteries are also popular with car manufacturers. The specific property of the nickel–hydrogen batteries is its long life: the cells handle more than 20,000 charge cycles on 85% efficiency.