When does a car battery charge?

Besides an alternator, the battery is one of the essential components in a car’s electrical system. It powers all the car’s electrical systems when the engine is not running. Even when the engine is running, it plays a vital role in the flawless functioning of the voltage regulator in the alternator.

Modern car electrical systems require a battery to function properly, unlike the outdated systems that used generators and could work without a battery. A dead battery will mean your vehicle won’t start, and the alternator will be forced to work extra hard to the point of potentially damaging it.

But with all the important roles a battery plays, have you ever deliberated when the car battery charges?

So, When Does A Car Battery Charge?

The car battery charges whenever the car is running. The alternator maintains a constant flow of AC power going into the battery, which keeps charging it. The alternator produces power every time the car engine is running. Similarly, the battery charges every time your vehicle engine is running.

However, this is when assuming that the battery is in proper health. There comes a time in the battery’s life when it no longer holds a charge. So if your car battery is in good condition, it always charges whenever the car engine is charging.

Now you might be asking yourself if a car battery charges when the car is idling. Yes! The battery also charges when the car is in idling mode again, assuming the battery is good and can hold a charge. As long as the alternator’s mechanical action is still going on and being rotated by the engine crankshaft, the alternator will keep producing AC current, hence charging the car battery.

How Does Car Battery Charges

A car battery charges in two ways, i.e., through the engine alternator when the car is running or using an external charger. An alternator charges the battery as long as the engine keeps running. This is why running most electrical devices such as dome lights or radio when the engine is off can deplete the car battery, but it gets replenished automatically when you start the car.

The alternator is the car’s powerhouse and is connected to the engine’s crankshaft through a belt. When the car engine is running, the crankshaft rotates the belt, which in turn rotates a rotor, surrounded by magnets in the alternator. As the rotor spins past the magnets, it produces AC current converted to DC current to power the electrical systems and components throughout the vehicle and, lastly, charge the battery.

As the engine’s RPM increases, the ability of the alternator to produce electricity also increases, and any power that is not being used by accessories such as headlights is used to charge the battery. An external charger is the best option when a car battery dies to charge it back.

How Long Does It Take To Charge A Battery When The Car Is Idling?

This is one of the questions being asked by many people, particularly during the current corona pandemic when most vehicles are sitting in the parking lot longer. This makes it a good idea to allow your engine to idle to recharge the battery. But how much time does it take to charge the battery when the car is idling fully.

According to an experienced electrical engine, you need to leave your car idle for more than one hour to charge your battery completely. A car has many electrical systems, with each vying for some power from the alternator. This means there is only small energy left to recharge the battery.

However, some of the factors that might affect the amount of time it takes for the battery to charge include; the number of electrical and computer systems in your vehicle, the amount of power voltage produced by the alternator, and the battery’s condition.

Generally, allowing your engine to idle might charge your car battery a bit, but it is not the best way of charging the battery. It is hence a better idea to take a drive instead of keeping it idling. If your car has been in the parking for a while, the best solution is to put an external charger to maintain a low voltage amount applied to your battery to prevent it from going flat or dead. 

How Long Does It Take A Battery To Charge While Driving?

So, your car has stayed in the parking lot for too long until the battery has gone flat. After jump-starting it, you might be wondering how long it will take the battery to charge while driving. In general, you need to drive your car for a minimum of thirty minutes to get a significant charge on it.

However, this does not mean that a 30 minutes’ drive will recharge your battery fully. You should consider some factors, such as; how much the car battery was depleted and the overall condition and age of the battery.

If your vehicle’s engine has not been sitting for long without running the engine, driving the car for only thirty minutes might not recharge the battery completely. But it will still put a significant charge on the battery and prevent it from going dead completely.

Sometimes, with time, the battery becomes worn out and starts to lose its charging properties. This makes the battery not hold a charge any longer. This means even if you drive for hours, the car battery will not hold any charge anymore. If this is the condition of your battery, it is time to have it replaced.


The electrical system of a vehicle is a bit complex. However, we hope that you now understand when a car battery charges and how it occurs. The car battery is only a single component in the complex electrical circuit, and if it no longer charges, you just need to replace it with a new one. However, the car alternator is the actual electrical power plant, so it is a lot more expensive and complicated to repair if it gets damaged.

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