Does a car battery charge itself?

By Martin Pretorius 

Car batteries are usually treated as fit-and-forget items, only getting any attention when they go flat or malfunction in some other way. But, contrary to what some motorists may think, a car battery doesn't charge itself – it relies on a healthy electrical system to support the quest for a consistent performance. Take away the support system, and a car battery will run flat in short order, just like a cell phone or TV remote would. 

What keep a car battery charged?

Every time a car's starter is operated, or a window wound down, or someone plays the radio without the engine running, the car's battery loses some charge. Even without any such loads, car batteries will eventually run flat, due to a phenomenon known as the battery's internal resistance.

This is a common trait with all batteries (even a switched-off cell phone will eventually lose its battery power), and must be counteracted by the charging system. In a car, the most important component in the charging system is called the alternator. The alternator is mounted on the engine, and is tasked with converting some of the engine's power into electrical energy to recharge the battery.

The alternator is the key component.

Because the alternator is driven from the engine by a belt, it will generate this replenishing electrical current whenever the engine running, thus helping to maintain a constant charge in the battery. This way, there will always be enough electrical power to turn the starter motor and energise the engine control system, ensuring a quick, reliable start.

Pay close attention to the little “battery” warning light in your car's instrument pack: if it illuminates while you're driving, that means that the battery isn't receiving its recharging current. There are many possible reasons for this (most often it's due to a broken or slipping alternator drive belt), and the cause of the problem must be repaired as quickly as possible. Failure to do so will damage the battery (and possibly electronic components as well), leaving you with an unnecessarily inflated repair bill. And remember, if you're in doubt, stop at your nearest battery specialist – they have the know-how and equipment to keep your car energised.