What component is typically responsible for charging a truck's battery?

The alternator is the component responsible for charging a truck's battery while the engine is running. It converts mechanical energy from the engine into electrical energy, which not only powers the vehicle's electrical systems but also recharges the battery. When the engine operates, the alternator generates electricity that replenishes the battery's charge, ensuring that it remains fully charged to start the engine and run electrical accessories.

Other components such as the starter motor have a different function; it is designed to crank the engine during the start-up phase but does not produce electrical energy for charging. The battery charger is an external device used when the battery is not in the vehicle, serving to recharge it when needed. The fuel pump, on the other hand, is responsible for delivering fuel from the tank to the engine and has no role in the battery charging process. Thus, the alternator's primary role in maintaining the battery's charge during operation makes it the correct answer.