What is the primary function of a vehicle's battery?

The primary function of a vehicle's battery is to provide the electrical energy needed to start the engine. When you turn the ignition key or press the start button, the battery sends a surge of power to the starter motor, which is responsible for turning the engine over and initiating the combustion process. This action is crucial, as without the battery's initial power, the engine would not be able to start.

While there are other systems in the vehicle that rely on the battery for energy, such as the lights, radio, and electronic systems, those functions occur after the engine has started. The battery's primary role is focused on the starting process itself, making option C the most accurate choice regarding its main function.