An automotive battery is a rechargeable battery that supplies electric energy to an automobile. Traditionally, this is called an SLI, for starting, lighting, ignition, and its main purpose is to start the engine. Once the engine is running, power for the car is supplied by the alternator. Typically, the ignition discharges less than three per cent of the battery capacity. SLI batteries are designed to release a high burst of current, measured in amperes, and then be quickly recharged. They are not designed for deep discharge, and a full discharge can reduce the batterys lifespan.