Maintenance Overview: Battery
The automotive battery is an electrochemical device that produces voltage and delivers current. In an automotive battery the electrochemical action can be reversed, recharging the battery, providing many years of service. Batteries emit hydrogen gas while charging and the battery case cannot be completely sealed. Batteries (maintenance free) have small vents on the side forcing the gases to go through baffles to escape. This process allows the liquid to condense and flow back to the bottom of the battery.
The purpose of the battery is to supply current to the starter motor, provide current to the ignition system while cranking, to supply additional current when the demand is higher than the alternator can supply and to act as an electrical reservoir. Batteries are rated in cold cranking amps. This represents the current the battery can produce for 30 seconds at 0 degrees before the battery voltage drops below 7.2 volts.