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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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  • A good read

    A good read

  • Very helpful

    I had a low battery but after charging for a few hours it did start. I needed to know if it was then worth leaving it ticking over for a few hours to boost it further but didn't know if it would charge just on tickover at all. You answered my question , it does. Thank you. Paul C

  • Agreed

    As what was mentioned it does charge the battery when idling however it will charge more efficiently when the vehicle is at a certain rpm. Where the alternator is rotating at a higher rpm to charge the battery. Also you can find out if your alternator is charging properly from this article here . Using a voltmeter or a multimeter also helps identifying when alternator is charging the battery properly.

  • Wrong answer??

    I think he didn't get the question. I think what they are asking is can hook up a battery charger to the battery while the car is running. Will it charge faster while running with a battery charger hooked up? Or could this cause a problem?

  • Response to Richie

    Hi Richie, the article refers to charging your battery while idling, but without a charger. Thank you for your feedback.


    Thank you for stating this because other battery places and articles claim it will not charge at idle. Interstate actually said idling will deplete the battery. Check it out, about half way down the page:
    That isn't the only incorrect statement in the article, and batteries is their business yet apparently they have no clue about usage. Or they're just trying to scare people into buying new batteries and/or chargers. Since the company exists to make $, I'll assume the latter, and they're willing to lie to do it.
    The short answer, imo, is yes, idling will charge the batt on virtually any car. The long answer is every car and conditions are different, so an old crappy car with a questionable alternator idling in >100F heat with elect fans and AC full blast may have trouble. It also matters if the car is in park/neutral or drive. A car under those conditions may be just fine in neutral but not in drive. Otherwise, any car made in the last 50 years that is working normally will charge, even in drive. They may charge very quickly, like my current car, or it may take many hours. Every car I've ever owned can charge at idle unless the voltage regulator was bad. I've never had an Alt fail, only the regulator. I did see a bad Alt once, but just the one.
    Many people/places will say an Alternator not a battery charger, that's it there to run the car and only "top off" the batt. An Alt can not only charge a battery, it's an excellent charger and is more powerful that most chargers you can buy. Optionally, you can look at the generators that make the power feeding your store bought charger, and the computer you're reading this on. They are virtually identical to your cars alternator, just larger and wired to make more voltage.

    Richie; I don't think that was the question but yes, you can use a charger while idling. It won't help as much you might think, and may not help at all, but it won't hurt. It all depends on the alternator, voltage regulator, battery voltage and charger voltage. If it's idling at 14.7V, like mine does, adding a charger that outputs 14.7 will almost certainly do nothing. If the Alt is feeding it say 13.7V then adding a charger making 14.7 will likely tell the voltage regulator to throttle back and reduce Alt output. In that case you may end up charging less, or more, or break even. Too may variables so you'd just have do it and measure current to find out. A trickle charger won't have much effect, but if you have a heavy duty 20A charger it may turn the Alt off altogether. Either way you're charging so no worries.
    What you won't find in articles like this is you can also trick the Alt into outputting more power, if you wanted, so it takes less time to charge. You can also modify chargers, or make your own, that will charge faster. Most people are aware that a charger will charge quickest when battery voltage is low, then as voltage rises they charge slower and slower. Cars do the same. This is annoying if you want it done asap. I prefer chargers that charge full blast all the time, but they don't make them for the general public because you need to know what you're doing. Eg; if you have a charger that makes 20A no matter what and put it on your car battery overnight, it may only ruin the battery, or it may catch fire and/or explode. So almost all chargers sold to the public are "safe", which means they take substantially longer. How to trick your car or make a charger like I described is something you'll have to learn yourself because it's a bit much to explain here, plus I'm sure the mod would delete the post.

  • Wrong question

    The question "Can you use a battery charger while the car is running?" on Google results leads you to this blog. So Ritchie is not wrong. Probably due to a mistake on the SEO.