An automotive battery is a rechargeable battery that supplies electrical energy to a motor vehicle.
its main purpose is to start the engine. Once the engine is running, power for the car's electrical systems is supplied by the alternator. Normally, starting discharges less than three per cent of the battery capacity. batteries are designed to release a high burst of current and then be quickly recharged. They are not designed for deep discharge, and a full discharge can reduce the battery's lifespan.
As well as starting the engine battery supplies the extra power necessary when the vehicle's electrical requirements exceed the supply from the charging system. It is also a stabilizer, evening out potentially damaging voltage spikes. While the engine is running, most of the power is provided by the alternator, which includes a voltage regulator to keep the output between 13.5 and 14.5 V.