Does A Car Battery Charge While Idling?
Today, we’re checking out the answer to the question: “Does A Car Battery Charge While Idling?”.
If you’re asking this question, you probably want to get more charge in your battery and you’re wondering if just idling the engine is enough, or do you actually need to drive the car for the battery to get any decent amount of charge?
Well, that’s exactly what we, the UK’s car battery experts, answer below.
Read on, Macduff.
Answering: Can You Charge Your Battery At Idle
So, the short answer is:
Yes. Yes, your car battery does charge while you’re idling.
There’s a bit more you should know, and we’ll go on to discuss.
What happens when you’re idling?
Idling is simply running the car’s engine while at rest.
If your car’s engine is running, it’s powering the alternator. You car’s alternator then charges the battery, as well as supplying power to the car’s electronics.
So even if you’re not moving the car, the running of the engine charges the battery.
How much charge does idling give to the vehicle battery?
This is the key question.
And the answer is, not a lot.
Idling charges the battery but it’s not exactly a flood of charge.
Technically, you could fully charge a battery just from idling, it’s just that it would take quite a long time.
So the question that naturally comes up is: is it actually worthwhile to idle the car to charge? In other words, is it beneficial to the battery? So…
Should you idle your car to charge the battery?
And the answer is: yes, but only if you do it long enough.
Some studies have shown that you need to charge the battery for at least 15-30 minutes to make up for the drop in charge caused by starting the engine!
So, to be safe, you’ll probably want to do it for at least 30 minutes so that you know it’s actually having a positive effect on the battery charge.
How does running the engine charge the battery?
Running the engine turns the alternator pulley, which causes an alternating current to be passed through a magnetic field.
This generates an electric current, which passes through the rectifier, converting it to a DC (direct current) supply.
How can I test if idling is charging my car battery?
Get a car battery tester, that’ll give you not just the battery voltage but also the battery health, so you’ll know the state of the battery and can replace it before it fails. (Here are the UK’s best vehicle battery testers)
Even a pretty cheap voltmeter can also be valuable. Or consider a car battery monitor – that attaches to your battery and can be accessed via an App (connecting via Bluetooth) at any time. Just go to the App and it’ll show you the voltage.
If the voltage reaches around 12.5-12.8V then it’s reached full charge. That’s what you want.
Too high a voltage could be an indication of a problem with your alternator or electrical system. And if the voltage is never reaching this range, then it could be in poor health – a battery tester, not just a voltmeter, can diagnose this.
If you want to test that idling is actually working, here’s how:
- Use the car battery tester (like these Topdon 12V battery testers) or voltmeter and measure the voltage of the battery before you start idling
- Idle the car for 30 minutes to one hour.
- Allow 20-30 minutes for the battery to cool down. Then test the battery again using the tester/voltmeter
If the battery voltage has increased significantly, then you know idling is a good option for you to charge the battery.
If voltage has not increased by much, then you either need to increase the time you’re idling for, or you need to consider one of the alternatives below to give your battery a fuller charge.
What are the alternative solutions for charging the battery?
As we said earlier, idling charges the battery but not that well.
There are two much superior ways, that give a lot more charge to the battery.
And they are:
1. Taking the car for a drive, ideally 15 minutes or more
Going for a drive in the car charges the battery more fully. Pushing the accelerator and moving the vehicle turns the alternator pulley faster, providing a higher AC current and thus a higher DC current. Higher current means a more powerful charge.
Of course, there are a couple of downsides to this method:
- It uses up your time. You have to actually drive the car, unlike idling where you can just leave it running for a while and go do something else.
- It uses up petrol. Not great for the environment. And petrol is far from cheap.
2. Using a car battery charger
Surely the best method. Modern smart chargers are literally set and forget. You don’t need to worry about overcharge, overheating or damaging the battery.
The top chargers, such as those made by CTEK (most notably, the CTEK MXS10) and NOCO (exemplified by the Genius 10UK charger) have really smart internal control units that monitor all aspects of the battery. They sense the level of charge and know exactly how much charge to put into your car battery at any given moment.
They can act as a trickle charger, just topping up the battery with what it needs. Stopping at time; and giving it a top up charge when necessary.
Here are the best car battery chargers in the UK for 2023.
They also have desulfation modes (CTEK, for example, have the famous Recond Mode). That mode removes sulfation (the gathering of lead sulfate crystals) from the battery plates. Sulfation is the No.1 cause of death of batteries, and these modes can extend your battery lifespan by 2 or 3 times!
There’s also a product called a battery desulfator that stays permanently attached to the battery, preventing sulfation from building up in the first place.
How often should you idle to charge your car battery?
We’ve gone into a lot of detail on how long car batteries last without the car being used.
Here’s a table giving you a rough estimate on how long the battery will last, depending on the battery condition, and a few other factors.
| Car Battery Age | Car Battery Condition | Parasitic Drain | Weather Conditions | How Long The Battery Lasts Without Driving – Estimate |
|---|---|---|---|---|
| 1 year old or less | Regularly used & fully charged often | Low levels | Mild weather (not too hot and not too cold) | 6-8 weeks |
| 1-2 years old | Regularly used & normally gets a full charge | Moderate levels | Quite hot or quite cold | 4-6 weeks |
| 3-4 years old | Irregularly used & only sometimes gets a full charge | Moderate levels | Quite hot or quite cold | 2-3 weeks |
| 4-5 years old | Occasionally used & often doesn’t get a full charge | High levels | Very hot or very cold | 2 weeks or less |
Whether idling is effective depends on the condition of your battery and the extent of any parasitic drain.
Parasitic drain is the charge consumed by electrical accessories even when the engine is off. It’s caused by:
- systems such as alarms, which must be kept on all the time, even when the engine is off
- Computer systems and radio, which have memory presets, which requires a constant source of power to be maintained
- Dashboard clocks, temperature gauge
As a general rule, you’ll want to idle the engine at least once every 2 weeks. And as we said, aim for at least 30 minutes, and ideally closer to the hour.
In most cases, that will increase the battery voltage – in other words, increasing its charge.
Here’s more info on car battery voltages and what they mean.
If there’s excessive parasitic draw, or your car battery is in poor condition, it may need more than that. Or you may consider one of the alternative charging methods mentioned earlier.
Does A Car Battery Charge While Idling Summary
Hope this article helps!
Hopefully you now know the answer to the question: Does a car battery charge while idling?
As you read, it certainly does.
Now, does it mean you should? Well, that’s what we discussed.
There’s a way to check whether idling actually improves your battery charge, by measuring the voltage before and after you idle the car.
Whether idling is worthwhile depends on factors like:
- the condition of your vehicle battery
- the condition of your car’s electrical system – does it have excessive parasitic drain?
- Your alternator condition
Good luck with your decision on whether idling is the best solution for your battery.