A car battery is a rechargeable power source that provides electricity to start a vehicle's engine and power its electrical systems. Typically made of lead-acid, it stores energy chemically and converts it into electrical energy when needed. When you turn the key in the ignition, the car battery sends a burst of electricity to the starter motor, allowing the engine to start. Once the engine is running, the alternator recharges the battery while powering the car's electrical components, such as lights and radio. Proper maintenance can extend a battery's lifespan.