Testing your car’s battery with a multimeter is easier than you’d think. And it’s a great thing to do once in a while. Especially before cold weather, since you especially need a reliable battery for a fast start in those cold mornings.
Before we start, you will work with a battery. Make sure not to rest anything metallic on the battery and never touch the two terminals together with a wrench or anything. Stay safe!
How to test a car battery with a multimeter
- Make sure your car has been sitting parked for at least 2 hours. This is so we can get a proper resting voltage.
- Open the hood and locate the battery. On some modern cars, it has a plastic cover.
- Grab the multimeter and set it to DC voltage (the V with a dashed and solid line above it see below photo with yellow markings), and the dial at 20. This will allow you to accurately measure between 0 and 20 Volts.
- Touch the red multimeter probe to the positive battery terminal (usually also red), and the black multimeter probe to the negative battery terminal (also black, most of the time).
- Ideally, you should get a reading of at least 12.6 V. A reading of 12.2 V would mean your battery is actually 50% charged. A reading of under 12 V means that… well… that’s a discharged battery. (and if you get a value with minus, you’ve mismatched the positive and the negative battery terminals)
Test your car’s alternator with a multimeter
And while you’re here, you can test your car’s alternator too!
The role of the alternator is to produce electricity and charge your battery. Also, while you’re driving, it can also take over and deliver power to your car’s electrical systems.
Just do the test outlined above while the engine is running. Be wary of any moving parts, like a fan or belts! Don’t hurt yourself.
A reading of 13.8V to 14.4V when your car is idling represents a healthy charging system, and everything is OK. Anything else and you should check with your mechanic.
So that’s about it! Checking your battery with a multimeter is quite an easy task. And knowing what the values mean, can save you from a bad time.
If it helps, here’s everything wrapped in a neat little table:
|Method of testing||Reading||Meaning|
|Car turned off for more than 2h||at least 12.6V||Everything is Ok|
|Car turned off for more than 2h||12.2V||50% battery charge|
|Car turned off for more than 2h||under 12V||Battery discharged|
|Car idling||Between 13.8V and 14.4V||Everything is Ok|
|Car idling||under 13.8V or over 14.4V||Consult a mechanic|