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Does idling a car drain the battery?

Do Car Batteries Charge or Drain While Idling? (Explained)

Do you let your car idle for a couple of hours? Have you ever asked yourself if your car batteries get recharged if your car engine is idle? Let’s answer these questions.

So do car batteries charge or drain while idling? Ideally, car batteries get recharged while idling. If your car battery is not charging, some other issues are causing that situation.

Today, we will learn more about whether car batteries charge or drain while the car engine is idle. Let’s start.

Table of Contents

Do Car Batteries Charge or Drain While Idling

Do Car Batteries Charge While Idling?

Today, most of the talk is about how or why a car battery dies. Let us talk about whether car batteries are charged while idling. If you ask whether car batteries get charged while idling, the answer to this is yes.

Car batteries do get charged while the engine idles. Of course, this can be done if there are no damages to the battery and if the car battery can still hold a charge. If there is a mechanical action in the alternator, the alternator is then producing AC current.

This will then cause the battery to charge even if the engine is idle. This is an interesting fact because almost all drivers do know this.

They do not know that car batteries can get charged even when the car’s engine is idle. What you have to consider is the status and the condition of the battery.

Can Car Batteries Drain While Idling?

If you are letting your car idle, this will recharge your car’s battery rather than drain it. However, if letting your car idle is draining your battery, there are some issues with that situation. If your car is idle, the engine and the alternator will then run slowly.

The alternator will then provide just enough electricity so that the battery can be charged. If your car is idle causing your battery to drain, there can be problems with the alternator.

If the alternator has problems, it will have minimal charge to no charge at all. So instead of recharging the battery, your car battery will get drained. There is also the issue of high-powered electrical accessories.

Accessories such as car stereos or headlights can put a higher load on the alternator. If you put on accessories that require a higher load on the alternator, this will automatically drain the battery.

How Long to Idle a Car to Charge Battery?

Now that you know that letting your car’s engine idle can charge your car’s battery, the next question would be how long it takes for a car’s engine to charge its battery. Our situation today would require us to let our cars sit in the garage.

We are spending less time outside driving around and more time in the house. So for your car battery recharge, you will not let your car’s engine idle for a couple of hours. You will need several hours to recharge your car battery completely.

This is an excellent question because some people hate to let their car idle. Letting your car idle can do good to your car’s engine. However, letting your car idle for years can do damage to your car.

So you have to let yourself idle for a couple of hours. These couple of hours will then recharge your car battery completely.

Is Idling the Best Way How to Charge the Battery?

Though many people are letting their car engine on idle to recharge the car’s battery, this is not the best way to charge the battery for all drivers. Drivers are diverse, and each of them has its preferred way of charging its battery.

Though this is an excellent way to charge your battery, it is not recommended by everyone. Modern cars have battery management systems. This is made so that the car batteries of the vehicle will last longer.

Some experts and drivers would say that letting your car idle for some time will soon drain the car’s battery. Some people say that cars are not made to put idle to recharge their batteries.

Letting your car idle for a couple of hours will cause your car to have a lack performance. So while idling your car’s engine can recharge the car’s battery, it is not the best way to charge your batteries.

idling car

What Are the Reasons Why Is Your Battery Isn’t Charging While Idling?

If your car battery is not charging while on idle, people would automatically jump to a broken battery. But the truth is that it is the alternator that has problems. Here are some common problems of an alternator, causing the battery not to charge.

1. There Can Be Computer Error

Modern cars have a central computer system or engine control unit. These are the one who manages the components and parts of a car. This computer system also manages the alternator.

So if there is a charging error, this will contribute to a malfunctioned alternator. This will then prevent the car battery from charging.

2. There Can Be A Bad Alternator Or A Bad Battery

Alternators and batteries are also needed to be replaced. These do not go on forever. Like some other engine parts, they also need to be replaced.

Your car’s battery can be up to two to five years. However, this will depend on how good the car maintenance is and how often you drive your car. So if this is the case, you might need to replace your alternator or battery.

3. There Can Be Wiring Issues

The alternator has multiple wirings. These wirings help in giving producing power for the alternator. If there will be at least one wire that will get disconnected, the alternator and the car battery will not recharge.

4. There Can Be A Blown Fuse

Many car models rely hugely on a single fuse. But fuses also do not last for so long. The fuses can get old and can even blow up.

If that will happen, the alternator will not be able to charge anymore.

5. There Can Be A Damaged Belt Or A Damaged Pulley

The mechanical power comes from the belt or pulley. This mechanical power will then be converted to electrical energy.

If the belt is stretched out so much, this belt or pulley can get damaged and snap apart. This will then cause the battery not to be charged.

What to Do If Your Car Battery Isn’t Charging While Idling?

If your car battery is not charging and will not hold a charge, here are some things you can do for that matter. You can check the headlights. You can get through this by the process of elimination.

Turn on the headlights. If the light is good and steady, your battery is okay. If the light is not good and weak, then you might have a problem with your battery.

But if the light is good, you might have problems with the wirings or a faulty starter. You can also do and attach a voltmeter.

You also have to consider the battery. Replace the battery if it is necessary.


In summary, letting your car engine idle can recharge your car batteries. You will need to let it idle for a couple of hours so that your car engine can get recharged. There are, however, some cases where your battery will not recharge; if this happens, there might be some other problem.

The first thing to do is look and check for the alternator of the vehicle. This is the number one possible reason why your battery is not charging.


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Do Car Batteries Charge While Idling?


If you don’t take regular journeys in your car, you might find that your car’s battery is starting to lose charge faster than you are replenishing it. This can damage the lifecycle of the battery and eventually result in your car not starting.

If you don’t want to invest in a car battery charger, you might decide to try and charge your car’s battery by leaving your car idling. But, do car batteries charge while idling? You can also read about AGM batteries and their advantages.

Does the Battery Charge if You Let the Car Idle?

The simple answer to this question is yes, your car’s battery will start to charge as long as your engine is running. As long as the electrical systems aren’t draining the battery quicker than the alternator is charging it, it is technically possible to completely charge your battery using this method.

How the Alternator Charges Your Car’s Battery

To explain this in more detail, we’ll need to talk about one of the key components in your vehicle — the alternator. The alternator is basically a generator, or dynamo that is driven by the belt from the engine.

When the engine is running the alternator will use this rotation to generate electricity inside its coils. This alternating current is then turned into a direct current which is then used to recharge the battery. As long as the engine is running, this process will occur. However, if you find your battery is starting to lose charge and can’t work out why, your alternator could be the problem.

How Long To Idle Car To Charge Battery?

While it is technically possible to charge your car battery by just idling, it’s not very efficient. You’d likely have to leave your car running for hours to even come close to a full charge. This is due to the amount of charge that is initially lost when cranking the engine. Some studies have shown that it can take between 15-30 minutes to recoup this initial charge.

If you can, a much more efficient way to charge your battery would be to take your car out for regular journeys. How long to drive to charge battery can depend on the vehicle and the type of battery it uses, but you will usually find it will charge faster this way. If you aren’t able to do this, investing in a trickle charger is a great way to keep your battery both healthy and full of charge.

How To Know Whether a Car Battery Is Charged

You may also be wondering, how long does it take to charge a car battery? It’s hard to say exactly how long it takes to fully charge a car battery, but a good way to check the current charge is through the use of a multimeter.

A fully charged car battery should measure at 12.6 volts or higher when not in use, and between 13.7 volts and 14.7 volts when the engine is running. If you have a lower voltage than this, your battery may need to be charged, or even replaced.

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