How Long To Leave A Car Running To Charge The Battery?

You just got back from a long day and you’re ready to go home, but the battery is dead. How long should you leave your car running so that it will charge? The answer depends on how much power is left in the battery.

If there’s at least 10% of charge left, then leaving your car running for 30 minutes should be enough time to get it charged up. If you’re like me, every time your car battery dies and you need to charge it, you question how long to leave a car running.

You might think that the amount of time needed is somewhere between 10 and 15 minutes for most batteries, but this isn’t always the case.

It really depends on what kind of battery you have in there, In this blog post, we will discuss how long to leave a car running so your battery doesn’t die again.

Battery Basics:

First things first, let’s get up to speed on the basics of batteries. Your car battery is what starts your engine. It does this by producing an electric current using chemicals in the battery cells. You can think of these cells as tiny power plants inside the battery.

When you start your car, something called a starter motor turns on. This is what actually starts the car spinning. When it’s running, it spins a shaft attached to your engine crankshaft.

The starter motor then works with some gears that are mounted onto this crankshaft to get everything turning quickly enough that your car can startup.

Now you’ve got the basics of how batteries work under your belt. Hopefully, this will help you understand the next section.

Battery Efficiency

Between how long it takes your engine to warm up and just general wear and tear on your car, you are constantly losing energy. This is why most cars have larger batteries that are designed for this purpose. The real question is, what happens to your battery during these periods of time?

As you drive your car, it heats up the engine and also puts energy into moving parts. Because these parts are now warmer than before, they require less energy to move them around.

This means that less power is needed by your battery, Of course, at some point, it’s still not enough to keep your battery charged so you’re going to need to keep it plugged in.

Check Your Battery Sticker

The type of battery you have is largely determined by how much power you want your car to have. You can get batteries that are less expensive and last longer or ones that give you better starting power but don’t last as long before needing a recharge.

Of course, there’s a tradeoff! Luckily for you, there is also some math we can perform to get a rough estimate of how long it will take your battery to charge.

If You Look On The Side Of Your Battery And Find Something That Looks Like This:

You’re in luck! This is called a CCA rating and stands for Cold Cranking Amps. CCA is how much power you can get out of your battery in cold weather conditions. This is actually one of the most important factors in determining the life cycle of your battery so it’s great finding this number.

Now, all you need to do is take that number and divide it by 20, then add 1 hour to that number. So, for instance, if your battery had a rating of 300 CCA then you’d have the following.

So to fully charge this battery after it has been drained, it’s going to take about 2.7 hours! Be sure to check on your car every 30 minutes or so just in case since there can be quite a bit of variation in this number.

If you’re like me, making sure it’s charged will be the first thing on your mind once you’ve gotten back into your warm car. You can then pat yourself on the back for having a quick charging battery since most batteries only take about an hour to charge at that point.

Who Can We Trust?

Finally, we have one more little bit of math to throw your way. All this time you’ve been reading various numbers and trying to make sense of them yourself but I bet there’s someone who makes doing this sort of thing much easier.

The reason why it takes longer for cars to charge in the winter is that your battery can’t get rid of heat as efficiently. The same goes for inside a car. Even if you don’t have a/c going, there’s still going to be some residual heat from the engine and moving parts.

You’ll notice this when you get out of a warm car because it will take a few minutes before you feel cold. Of course, that’s not enough heat to bring the battery up to full strength but it does help! This means that if your car is running then it’s going to charge more quickly than if it’s turned off.

This is why automakers recommend leaving your vehicle plugged in even if you’re not charging it that residual heat helps negate the need for you to leave it running.

It’s not quite that simple though, because if your car is running then you’re also burning gas which means all the extra energy will be wasted in order to make your car run.

What Are Some Signs That Your Battery is Dying?

  • Battery dies when you turn on the headlights
  • Battery dies while driving

Charge Symptoms:

The easiest way to tell if your battery is charging is to look at the dashboard for any lights other than the engine light or traction control. You can also pop your hood and listen for any hissing sounds from the alternator belt, this means the alternator is charging.

If you are having other problems with your vehicle, or if it often happens but not always there could be something else the issue. For instance, an ignition coil could be going bad and just needs to have a good charge every now and then to work properly.

There are many things that can go wrong with your car, but a dead battery is certainly common and easy to troubleshoot.

If your engine light turns on, pull over immediately and turn off the car, don’t drive anymore until you get it checked out by a mechanic.

What Are Some Other Ways To Maintain A Healthy Battery:

  • Do not let the battery drain down below 11.5 volts, this could kill your battery
  • Keep fluid levels up to par
  • Check all electrical components for corrosion and replace as needed
  • Don’t leave unnecessary lights on when you park or push start your car.

I hope you enjoyed this article and learned something new, Comments or suggestions for future articles are more than welcome. If you liked the article please share it with others on social media, etc. Thanks.


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Yusuke Kohara
By Yusuke Kohara

Hi, my name is Yusuke Kohara. I'm a research scientist with 20+ years of experience in the battery industry. My knowledge and expertise has been applied to power electric vehicles, mobile electronics, and more! I am also a true car enthusiast. It’s not just about cars for me - it's about all things automotive! I enjoy helping others find their perfect vehicle by providing detailed buying guides as well as reviews on different types of batteries from various manufacturers across the world.


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