Next to the alternator, the battery is the most important part of any car’s electrical system. It provides the energy to run all of your fancy electronics when the engine is not running, and when the engine is running, it plays a vital role in the proper functioning of the alternator’s voltage regulator.

Unlike old electrical systems that used generators and could function without a battery, modern automotive electrical systems require a battery to function properly. A dead battery means a car that won’t start and an alternator that’s working too hard, potentially to the point of failure. That’s why it’s so important to know how to properly and safely charge and maintain a car battery.

There are two ways to charge a car battery: with the alternator or with an external charger. Under normal circumstances, the alternator charges the battery when the engine is running. When a battery is flat, an external charger is the best way to recharge it.

This is why most normal battery usage, such as running the radio or dome light with the engine off, is naturally replenished the next time you start your car. As the engine RPM increases, so does the alternator’s ability to generate electricity, and any power not being used by accessories like your headlights is available to charge the battery.