How long should I let my car idle to charge its battery?

Have you ever thought about how long it takes to charge a car battery when idling? And is it safe to let the car idle to charge its battery? I did some research, and here is my answer.

It takes about 15-20 minutes to charge a car battery when idling. Assuming all the electricals, including radio, fans, AC, and headlights, are off. It does not fully charge the battery but enough so you can restart your vehicle.

How much charge your car battery is going to get when idling (or driving) vastly depends on various factors, including:

  • The health and age of your car battery.
  • The health of alternator (small generator that charges the car battery).
  • RPMs of the engine.
  • Condition of battery terminals.
  • Energy usage of other electricals inside your car.

Is it safe to let your car idle to charge the battery?

Letting your car run idle might create some problems. Most modern cars don’t even allow charging the battery at lower RPMs to protect the alternator and other electrical components. Although you can let your car run idle to charge the battery, it is not safe for the environment.

Especially if you are in a closed garage or parking lot and there is no ventilation. Internal Combustion Engines (ICE) produce carbon dioxide (CO2) and carbon monoxide (CO), which are harmful to humans and cause climate change and global warming.

Instead of letting your car run idle, you should go for a drive so the battery can charge faster.

If you do not drive your car all that much, you can opt for a battery charger/maintainer to keep your car’s battery topped off. These charges are smart and don’t damage or overcharge the battery.

A good battery charger can be bought from Amazon for less than $50.

Does revving the engine charge your battery faster?

Normally, cars idle at around 500 to 1000 RPMs which spins the alternator slowly causing it to produce less electricity. Revving the engine or driving at high RPMs causes the alternator to spin fast. It produces more electricity resulting in faster charging times of a car’s battery.

How long does it take to charge a car battery when driving?

Charging times depend on the condition of your car battery and its current charge state. If your battery is completely depleted, it can take about 2 hours to completely charge the battery to 80 percent. But, if the battery is good, it should only take around 15-20 minutes.

How to tell if your battery is charging?

There is a battery warning indicator LED on the dashboard of every car. If the battery voltage drops below 13 volts or rises above 15 volts, this warning indicator will light up. It means there is something wrong with your car’s battery or the alternator, and it is not charging the battery.

In older (or some newer) cars, there is a battery gauge/meter on the dashboard. After starting your car, the battery gauge should read between 13 and 15 volts. If the voltage reading is out of this range, you should get your car’s alternator and battery inspected and fixed.

You can also test the voltages of your car’s battery manually by using a very basic multimeter. Refer to the following video for testing your car battery yourself.

A car battery lasts around 4-6 years. If your battery has reached its lifespan, you should replace it.

How long does a car battery last without being charged?

Charge holding capabilities of a car’s battery depending on its age and health.

A good car battery should easily hold its charge for about a month if the car is left undriven.

Take this number with a grain of salt. Modern cars have complicated electronics and advanced security systems that might drain the battery more than others.

A typical good car battery should hold a charge for at least 3-weeks before it needs recharging/maintenance.

If the battery in your car has reached its threshold, it is time to replace it.

Car batteries contain lead, which should be recycled properly. You can contact any auto parts store, and they will recycle your old battery for free. Some might even give you credit for your next battery purchase.

If your battery is good, but you do not need to drive your car very often, you can use a battery charger/maintainer. These car battery chargers won’t overcharge or damage your battery and are widely available in auto part stores and on Amazon.

Sources:
Effects of alternator speed to car charging system
Toxic exhaust emissions
Recycling lead acid batteries

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About Frank Diaz

Hi everyone, my name is Frank Diaz and I am the face behind GaragestPicks. I studied Mechanical Engineering at Georgia Institute of Technology and worked as a mechanic for over 20 years. I love working on cars and doing DIY projects around the house. I write this blog to share my knowledge and help others fix their cars with most common tools.

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