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Does a Car Battery Charge When Idling?

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Car battery installed

The everyday driver has so many questions about their car. Since your car doesn’t come with an FAQ sheet, I’m here to help out. In today’s blog, we’re exploring the idea of charging a car battery and whether or not it can be done while idling.

If you didn’t even know car batteries automatically recharge, then get ready to have your mind blown. I’ll explain how it happens when it charges, and ways to extend your battery’s life. Let’s get started.

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Preface: We’re Not Talking About Electric Cars

Let’s just preface by pointing out that I’m not talking about electric or hybrid cars here. Any plug-in car clearly needs its battery to be charged.

This article is all about internal combustion (gas-powered) engines. In other words, cars that don’t have plug-in ports on the side for charging the battery.

Wait, Car Batteries Need to Charge?

You’re not driving a Tesla, since when do you need to charge your car? This concept might sound funny initially, but it’s the truth: car batteries need to charge.

Car batteries need to charge or else they’ll die. When batteries are simply plugged into a circuit, they will start losing power. It’s like AA batteries in a remote that you never use. Over time, the batteries will die.

The good news is that car batteries are built to recharge themselves as the car is used.


Who Does This Affect?

This idea of battery charging affects everyone who has a car. However, it’s especially useful information for people who live in a city, has multiple vehicles, or rarely use their car.

If you emerged from your home after a year-long lockdown, you’ll probably know what I’m getting at.

For people who are always hitting the asphalt with their daily driver, this problem really never arises. The car is always charging itself so the driver never thinks about it.

Once you go a long period without driving, your battery will probably be dead. A quick jump-start will bring your car back to life and sufficiently recharge your battery. It all works due to the chemistry going on inside your car’s battery.

Looking Inside Your Car’s Battery

Put down the Sawzall — no need to crack the top off of your battery, I’ll share with you what’s going on (not to mention that’s insanely dangerous to do).

At the end of the day, the goal of your battery is to make electrons which makes electricity. To keep things simple and affordable (even though batteries are getting more expensive), most car batteries use a lead-acid chemical process.

Your battery has a number of cells in it. For a typical 12V battery, you can expect to see around six cells.

In each cell there are two plates: one is lead, and the other is lead dioxide. They’re sitting in a sulphuric acid bath which helps the process go faster. All of these plates are assembled with dividers between them and a positive and negative terminal that feed into the battery.

This type of setup also allows electrons to flow in either direction. They can move out of the battery, but they can also go into it. What does that mean? Your battery can give away electricity but also accept electricity as a means of recharging.

Inside of a car battery

How the Charging Process Works

The whole charging process can be attributed to the alternator. In fact, the only job of an alternator is to crank in electricity whenever the car is running.

It’s an electrical-mechanical component and it’s a little tricky to understand. Basically, your car’s engine will spin a drive belt that’s connected to the shaft of the alternator.

As the belt spins, so does the shaft. When the shaft rotates, it engages with a number of windings, rectifiers, brushes, and slip rings.

When a magnet goes through a loop of wire, a current is sent through in a single direction. A coil is just a bunch of loops bunched up into a single piece. Since the rotor of the alternator is an electromagnet, you’re seeing the same phenomenon.

As the rotor spins, electricity is generated through the windings (coils of wire).

Finally, the generated electricity is regulated down to a certain voltage and passed to your car’s battery. Voila, the battery is charging.


Does a Car Battery Charge When Idling?

As covered previously, a car’s battery will charge whenever the engine spins the belt tied to the alternator. Assuming the alternator, engine, belt, and battery are all in working order, then yes, a car battery will charge when idling.

The only caveat is that it doesn’t really “charge” that fast. This is solely due to the fact that the engine doesn’t have a load on it when your car is simply idling.

In addition, idling RPMs are less than the RPMs when you’re driving down the road. The belt will spin slower, rotating the shaft slower, and producing less electricity to recharge your battery.

The battery still needs to recharge faster than it is burning electricity. Think about all the electrical components running while your car is idling:

  • The radio
  • AC system
  • Fuel pumps
  • On-board computers

If the electrical need for these components outweighs the juice that your alternator can pump in, your battery will still lose its charge. Although it’s technically still charging, it’s expending too much electricity.

For that reason, I usually suggest against simply idling if you’re looking to recharge your car’s battery. There are other ways to charge it.

Other Ways to Charge Your Car’s Battery

If idling isn’t doing it for you, you have some other options.

Use a Trickle Charger:

A trickle charger is a special piece of equipment that goes on your battery for extended periods of time. The idea is that it slowly feeds electricity into your battery, charging it.

This charger will plug into a wall outlet and has a positive and negative wire. You hook it up to your car when you’re not using it and that’s all.

Battery Tender Junior 12V Charger and Maintainer – Automatic 12V – 750mA Battery Float Chargers – 021-0123


Take a Lap (or Ten)

The best way to really charge your battery is by taking a few laps. Car experts say that you want to drive around 30mph for around 30 minutes. This seems to be the most efficient way to get your alternator churning and cranking electricity back into your battery.

I would also recommend turning off the radio and AC while you’re doing this. That will minimize how much electricity is siphoned away, resulting in a better charge.

Keep Your Battery Alive for Longer

If you’re tired of constantly coming back to a dead battery, I know your pain. In an effort to keep your battery alive for longer, try some of these tricks.

Remember to Turn Off Your Headlights

The best way to kill your battery is to leave your headlights on overnight. This is a huge power drain, and your battery isn’t smart enough to turn your headlights off. That is until the battery dies.

Automatic headlights are a great invention because it takes away the ability to forget and leave your lights on overnight. Still, you should get into the habit of checking your headlights before going inside for the night.

Turn Off The AC When It’s Not Needed

If you live in a mildly temperate part of the world, you might be able to avoid using your AC altogether. A moment of silence for our fellow Americans in Texas and Florida who can’t relate to this idea.

Still, you should minimize the use of your car’s AC. Remember that your AC pulls all of its power right from your car’s battery. Turning off the HVAC system when it’s not needed will keep your battery alive for longer. It also allows your car to charge more efficiently as you ride along.

Check Your Battery’s Health Every 6 Months

Checking your battery’s health is a great way to understand what’s going on under the hood. If you find out that your battery is dead or dying, you can replace it before things get ugly. Your car can struggle to start if your battery is on the fritz.

KONNWEI KW208 12V Car Battery Tester, 100-2000 CCA Load Tester Analyzer for Car Truck Marine Motorcycle SUV Boat


Stay Out of Extreme Temperatures

A battery in blistering heat or freezing cold will die quicker than one sitting at room temperature. If you live in an extreme climate, it’s a good idea to find a garage you can park in. Staying away from outside temperatures will ensure your battery’s life is maximized.

Clean Your Battery

If the top contacts of your battery get corrosion on them, your battery will start to fail. Put 15mL of baking soda in 150mL of hot water. Mix it together and use a toothbrush to apply it to the terminals of your battery. Scrub it until the batter is shiny.

Please make sure your car isn’t running when you’re doing this, and that you give your vehicle enough time to cool down. I wouldn’t want you to get hurt while you’re trying to clean your battery.

Car battery terminal corrosion
Car battery terminal corrosion

I would highly recommend disconnecting the battery terminal posts when cleaning the corrosion on both the terminals posts and the battery itself.

Also, to ensure no future corrosion buildup occurs, getting a pair of terminal pads and battery grease before re-connecting the battery terminal posts is a good idea.

If you’re looking for a heavy-duty battery terminal cleaner: Schumacher Battery Terminal Cleaning Brush

Schumacher Battery Terminal Cleaning Brush

Don’t Warm Up Your Car for Too Long

Some people make the mistake of using auto-start on their car and letting it idle for minutes to warm up. Around one minute is the most time you’ll want to warm up your car.

Any longer and you’ll just be wasting gas and taking away electricity from your battery.


You just found out that your car battery charges while idling. Though it doesn’t charge very quickly, it nonetheless still helps. We’ve reviewed how this happens, how your battery works, and other ways to charge your battery and make it last longer. For more car care tips, explore this blog. Make sure you have the right car accessories and tools for your ride.

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Ernest Martynyuk

An automotive enthusiast who's been tinkering with vehicles since I was 15-years old. Repairing automotive electronics has been my main job for over a decade now and have a passion for everything technical regarding cars.

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