Do Car Batteries Charge While Idling?

There’s nothing more annoying than needing to get somewhere, getting in your car, turning the key in the ignition, and discovering that your car battery is dead. One way to prevent such inconvenience is to keep the battery charged, but it’s not always clear whether you can do that when your car is stationary. So, does a car battery charge when your vehicle is idling, or do you need to go for a drive?

Car batteries do charge while idling because the alternator produces enough power to charge a battery when the car is in idle mode. As long as the car is running, the battery is being charged, albeit at a slower rate than when driving.

The rest of this article will answer all your questions about car batteries, from how to charge them to how to care for them properly. Everyone hates needing a jump-start, so it’s best to avoid being in that situation altogether! Reading this article and practicing what you learn will help prevent such a situation.

How a Car Battery Charges When Idling

Car batteries charge when a vehicle is idling because the alternator charges the battery when the car is running. Note that “running” doesn’t necessarily mean “moving”. A car can be running and still be stationary; that’s precisely what “idling” means.

As long as your car battery is in good health, all you need to do to charge is to keep your car running. As long as the engine crankshaft turns the alternator, the alternator produces an AC current that charges your car battery.

To completely charge your battery, you’d need to keep your car idling for several hours. The caveat is that it’ll take longer to charge because there are many systems in your car that rely on the power being generated by the alternator, leaving little charge for the battery.

Because of this, letting your car idle isn’t the most efficient way to charge your battery. The fastest way to charge a car battery is to go for a drive.

Why Do Car Batteries Need to Be Charged?

Car batteries need to be charged because they provide the electrical charge needed to start a car. They also function as surge protectors for the infotainment system and utilities (such as lights and wipers) by supplying power temporarily when the engine shuts down.

Car batteries are similar to the smaller batteries you use in appliances like your TV remote. All batteries, including car batteries, store chemical energy and convert it to electrical energy. In a car battery, that electrical energy starts the engine and powers things like lights when the vehicle isn’t running. Once the battery starts the engine, the car’s power is supplied by the alternator. 

The type of chemical reaction that occurs in car batteries is a lead-acid reaction. The battery has six cells, and each cell has two plates. One plate is made of lead and the other is made of lead dioxide.

The lead and lead dioxide plates are put in sulphuric acid, which is made of sulfur, hydrogen, and oxygen. These components cause a reaction that produces ions and lead sulfate. These react to the plate and produce hydrogen, triggering a chemical reaction that generates electrons. These electrons then make the spark of electricity your car needs to start.

If your car battery isn’t charged, the battery won’t be able to perform this reaction and provide the power to start your car.

Most drivers don’t need to think about charging their battery because they use their vehicle often enough that the batteries are always charging themselves. However, if you’ve multiple vehicles, live in a city, or simply don’t drive your car very often, you’ll need to keep the health of your car battery in mind to avoid the inconvenience of a jump-start.

How Long Do You Need to Drive to Charge Your Car Battery?

You need to drive your car for at least thirty minutes at highway speeds to sufficiently charge the battery. While driving for this period of won’t charge the battery to full capacity, it’ll give it enough charge to keep it from going dead.

The amount of time it takes to put sufficient charge on the battery depends on how quickly you’re driving, though. Faster speeds generate more revolutions per minute from your engine, recharging the battery faster. Therefore, you’ll need to be driving more than 55 MPH to get a decent charge on your battery.

You’ll also need to consider the health of your battery. Thirty minutes is the average length of time, but the charging period can be longer if your battery is extremely old or damaged.

How to Keep Your Battery Alive

If you notice that your car battery dies frequently, it may be time for a new one. But if you’re not ready to give up on your current battery just yet, there are some ways you can try to save it.

Here are some ideas:

  • Turn your headlights off when you’re done using them. Many vehicles now have automatic headlights, but not all do. If yours doesn’t have this feature, make sure you turn off the headlights when you’re done driving for the night. Leaving the headlights on, especially overnight, is a huge drain on your battery.
  • Turn off the air conditioning unless you need it. Your car’s air conditioning system pulls its power from your battery, so turning off the system will keep your battery from depleting too quickly. If you live in a mild climate, you may be able to stop using your AC completely.
  • Keep your car out of extreme temperatures. There’s a reason why car batteries die more frequently in winter: batteries that are in extreme climates die quicker than batteries that aren’t. If you live in an area that has blisteringly hot summers or freezing cold winters, it may be worth finding a garage to park一 if you don’t already have one in your home.
  • Clean your battery regularly. If the top of your battery gets corroded, the battery will fail. To avoid this, clean your battery by mixing baking soda with hot water and using a toothbrush to scrub the terminals of your battery.
  • Remove your car battery if you aren’t going to be using it. If you’re putting your car in storage, or if you don’t plan on driving your car for more than two weeks, you’re better off disconnecting the battery completely.

There comes the point when your car’s battery is completely dead, and none of the above tips will fix it. However, saving your car’s battery while you can is a great way to prolong its life and avoid needing a jump-start.

How to Determine if Your Car Battery Is Dead

You can pick up on various signs to determine if your car battery is dying or dead already. Here are some clues:

  • Your car won’t start. This is a telltale sign that your battery is dead. If it happens, you’ll need a jump-start.
  • Your engine struggles to turn over. Sometimes your car will start, but take a while to do so. A slight delay is acceptable in colder weather. But if it happens when the temperature hasn’t changed, it’s a sign that your car battery is weak.
  • Your headlights are dim, flickering, or nonexistent. The battery powers headlights. So if they don’t appear to be performing as well as they usually do, it might be time to check your battery.
  • Your check engine light is on. Ah, check the engine light. It could mean various things. But if it appears alongside other symptoms of a weak battery in this list, it’s probable that your battery is about to fail.
  • You notice an odd smell. If lead battery acid leaks, it emits a rotten egg small due to the hydrogen sulfide gas. This isn’t a good sign.

If you’re experiencing these problems, it’s best to bring your vehicle in to a mechanic to troubleshoot the issue.

The Different Types of Battery Chargers

If you don’t drive often and are worried about your car’s battery, you can invest in a charger to keep your battery charged even when you aren’t driving. Make sure that the charger you choose is compatible with your battery’s chemistry and that its voltage matches that of your battery.

If you’ve a lead-acid car battery, you’ll need a lead-acid charger. Similarly, an AGM battery needs an AGM-compatible charger.

Most car batteries are 12 volts, so you’ll need to get a 12-volt charger. However, bigger trucks use a 24-volt battery, so truck drivers need a 24-volt charger.

It’s also important to consider the charger type because if you charge your vehicle with the wrong charger, it’ll permanently damage the battery. There are three different types to choose from:

  • Standard
  • Trickle
  • Battery maintainers.

Standard chargers can put out between 1 and 50 amps in charging mode, whereas a trickle charger is a low amperage option that slowly charges your battery. The latter is better for your battery’s health in the long run.

Battery maintainers are small battery chargers that send small amounts of energy to the battery without you needing to do any activity. This expands the life of your battery and lets the battery maintain full charge. It’s a good option for people who have a vehicle they don’t drive frequently.


Your car charges your car battery every time it runs, so the battery will charge while the car is idling. However, this isn’t the most efficient way to charge your battery.

The best way is to drive at highway speeds or to use a battery charger if you don’t drive your car often. As long as you take steps to save your battery and drive your car frequently, your car battery will stay healthy for a long time.

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