The function of a vehicle alternator is to generate electrical power to recharge the battery and supply electricity to the vehicle's electrical systems when the engine is running. When the engine is running, the alternator converts mechanical energy from the engine's rotation into electrical energy. This electrical energy is then used to power the vehicle's lights, ignition system, audio system, and other electrical components. Additionally, the alternator continuously charges the vehicle's battery, ensuring it remains fully charged and ready to start the engine the next time it's needed. Overall, the alternator plays a crucial role in supplying the electrical power needed to operate the vehicle's systems and maintain battery charge.