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

The primary purpose of a vehicle's battery is to provide electrical energy to start the engine and power accessories. When the ignition is turned on, the battery supplies the necessary power to the starter motor, which cranks the engine and gets it running. Once the engine is running, the alternator takes over to supply power for the vehicle's electrical systems and to recharge the battery.

Powering accessories such as lights, radio, and other electronic components is also a significant role of the battery when the engine is off. While other components of the vehicle may use electrical energy for specific functions, the battery itself is essential for starting the engine and supplying power to the electrical systems during that initial phase when the engine is not yet running.

The other options misrepresent the role of the battery. For example, air conditioning systems typically rely on the engine's power and the alternator, rather than the battery alone. Fuel injectors are powered through the engine control unit and other related components, not directly by the battery. Brake pressure is maintained by hydraulic systems, which do not draw power from the battery, emphasizing that the battery's primary function is focused on starting and electrical accessories.