Car electrical systems in today's vehicles are more complex than that of their predecessors. The fundamentals are similar, but the components requiring power have increased. The vehicle battery is the workhorse of the vehicles electrical system. The battery provides cranking power to turn over the combustible engine allowing it to start. The battery's main function is to provide the power to start the engine. When the car is not running, the battery will provide power for the radio and other accessories. The alternator is also an essential part of the electrical system. The alternator through continuous rotation, as the car is running, provides power to operate the headlights, radio and so on. Look for battery dealers and local car electrical systems experts to have the battery's performance checked. The alternator also charges the battery as needed when the engine is running. The cars electrical system is direct current or DC. Direct current requires a circuit to provide power from the battery and a grounding circuit. The grounding circuit is the vehicle's frame.