Things To Know When Testing a 12V Battery with a Multimeter

Testing a battery with a multimeter is the best way to measure the state of charge when it’s not in use. As part of a regular maintenance schedule, it can help you identify problems before they start.

This article reviews how to test your 12-volt battery with a multimeter, along with details about what you should know when testing a 12v battery with a multimeter.

How Do You Test a 12V Battery with a Multimeter?

There are a few different ways to test a 12v battery with a multimeter. Still, the easiest and most accurate is to check the voltage across both battery terminals. This is often referred to as the open-circuit voltage.

The next method is checking for continuity using the ohms function. This will allow you to test for any shorts or breaks in the circuit of your 12v battery. A third option is to load test your battery by applying a known load and measuring the voltage drop. The last way to test your 12v battery is to use a hydrometer and measure specific gravity. (1)

mechanic turning on the voltmeter
Video | ChrisFix

Do You Need to Disconnect the Negative Cable When Testing the Car Battery?

We recommend you disconnect the negative terminal of your car battery before testing it with a multimeter, to make sure there’s no discharge while you are testing it. It also depends on your multimeter type and its settings. Suppose you have voltage settings with higher voltages than 12V. In this case, it is not recommended you leave your battery connected while testing it.

How Much Voltage Should a Car Battery Have?

A fully charged car battery should have around 12.6V or above. The ideal range for a fully charged car battery is between 12.4-12.7V and sometimes up to 13V after charging for several hours or leaving the engine running for about half an hour. However, a healthy battery voltage may vary from 12.2-12.8V depending on the battery type and brand, so it shouldn’t be a cause of concern if your battery voltage is near that range (the ideal one).

Why is my Multimeter Reading Low Voltage?

For starters, you could have a bad multimeter. If you have another one available, try testing it with that multimeter.

You could also be getting an inaccurate reading for a few other reasons:

1. There’s something wrong with your battery. For example, suppose there’s corrosion on the terminals of your battery. In that case, it can cause your multimeter to give you a false reading. Try cleaning off any corrosion with a wire brush if this is causing the problem. (2)

2. Your vehicle’s load can also cause your multimeter to read low voltage. For example, suppose your vehicle has an audio system installed in it. In that case, it will draw current from your battery even when you’re not using it. So when you’re testing your battery with a multimeter, make sure that all accessories are turned off: headlights, radio, audio system, etc.

Take a look at some of our related articles below.




References
(1) gravity – https://www.britannica.com/science/gravity-physics
(2) corrosion – https://www.sciencedirect.com/topics/materials-science/corrosion

Video References

ChrisFix

Automotive Tech

About Sam Orlovsky

b1d87d2ee85af3e51479df87928bdc88?s=90&d=mm&r=gI realized early on carpentry was a huge passion for me and I’ve stayed in the industry for over 20 years now. This gives me a unique ability to really be able to tell you what the best tools and recommendations are. I’m not only a carpenter but I also like machinery and anything to do with electrics. One of my career paths starting off was as an apprentice electrician so I also have a lot of experience with electrical products and anything related.