An automotive battery is a rechargeable battery that supplies electrical current to a motor vehicle. Its main purpose is to feed the starter, which starts the engine. Once the engine is running, power for the car's electrical systems is still supplied by the battery with the alternator charging as demands increase or decrease. Typically, starting uses less than three percent of the battery capacity. For this reason, automotive batteries are designed to deliver maximum current for a short period of time.Most car batteries rely on a lead-acid chemical reaction to get things moving and grooving. These batteries fall into the ƒ??SLIƒ? category. SLI stands for ƒ??starting, lighting, and ignition.ƒ? This type of battery provides short bursts of energy in order to power your lights, accessories, and engine. Even though lead-acid batteries are extremely reliable, despite the temperature changes, motion, and cramped conditions under your hood, a typical battery will only last around three to five years.