Device for storing electrical energy by a chemical process. In the normal car, this is a lead-acid battery, in which the chemical process is reversible so that the battery can be re-charged - impossible with dry batteries. Such batteries have a potential of 2 volts per cell when charged, so that most cars have batteries of six cells connected in series to produce 12 volts. A common battery rating is 56 ampere-hours, which means it should deliver 56 amps over a period of one hour or 1 amp over 56 hours.
Also see: How it Works - The Battery