How to Test Battery with Multimeter

Running into a dead battery is one of the most common problems that a car owner experiences. A battery test is necessary to decide whether a battery replacement is needed.

Many a time, it can be challenging to diagnose the issue. A cheap tool, such as a digital multimeter—can test the battery and let you know if your car battery is holding any charge. A multimeter can also check alternators that may adversely affect your battery.

In this article, we help you identify the health of the battery with the multimeter, along with providing answers to the following questions:

  • How do I know the car’s battery has gone bad?
  • Typically, what is the life of a battery?
  • In what situations is it not ideal to use a multimeter to check the car’s battery?

How Many Volts Are in a Car Battery?

After battery testing, the ideal voltage across a car battery should be 12.6 volts. Anything lower than 12 volts is considered a discharged or dead battery.

How to Test Battery with Multimeter

Steps to Test a Car Battery with a Multimeter

Testing batteries with a multimeter is a relatively easy and well-versed process. The result either tells you to charge your car battery or that it is time to replace the old one.

1. Remove a Residual Charge

car battery
Video | ChrisFix

Before testing the battery, leave the car running for an hour, minimum. This would help you get the most accurate reading of the battery’s voltage.

If this is not possible, turn on the headlights for a few minutes with the vehicle off. This would eliminate any residual charge your car’s electrical system may have.

2. Prepare Your Multimeter

preparing the multimeter
Video | ChrisFix

Make sure to get the correct reading for how many volts of electricity your car battery can produce by setting your digital multimeter to 20 volts. Select the lowest voltage above 15 volts on your digital multimeter if your multimeter doesn’t have that voltage.

3. Find the Car Battery

car's open hood with multimeter
Video | ChrisFix

To test a car battery, you’ll need to make sure that you can find the battery and its terminals first. In most vehicles, the battery is located under the hood in the engine bay towards one side of the engine. However, modern cars may have batteries in their trunk. If you cannot find it, you may consult the automobile’s manual or the car manufacturer’s website to determine the location.

Present-day cars have a plastic cover over their batteries that you may need to unscrew to access the battery’s terminals. Make sure to prevent anything metal, like tools, from touching the terminals since it may shorten.

4. Connect the Multimeter Probes to The Battery Terminals

connecting the multimeter probes
Video | ChrisFix

Connect each probe of the digital multimeter to the car battery terminals, negative to negative and positive to positive. Both—the multimeter and the battery—are color-coded. The negative terminal and probe will be black, and the positive terminal and probe will be red. If you are not getting a positive reading in the digital multimeter, you need to reverse them.

While some probes are metal pieces to touch, some are clips that are to be attached.

5. Check the Reading

The multimeter will show you the reading. Please write it down. Ideally, even after running the headlights for 2 minutes, the voltage should read close to 12.6 volts, or you may have a bad battery. If the voltage value is slightly higher than 12.6 volts, then it’s perfectly normal. If the battery goes down to 12.2 volts, it’s only 50% charged.

Anything lower than 12 volts is termed dead or discharged.

Even if your battery doesn’t have a bad charge, it’s wise to check if the car can draw power successfully.

6. Ask Someone to Fire up The Engine

Next, keeping the multimeter probes attached to the car battery, ask a friend to turn the car’s ignition. Ensure the vehicle is in neutral and the parking brake is engaged before starting the car. Also, any multimeter wire must not hang into moving belts or pulleys on the engine.

This is a two-person job; one must keep an eye on the multimeter for the fluctuations, and the other must take control of the ignition. Try not to do it all by yourself, or you may record an incorrect reading.

7. Check the Reading Again

checking the reading on multimeter

Ideally, as the car tries to start, the voltage must initially drop to 10 volts. If the reading falls below 10 volts but stays above 5 volts, the battery will die slowly and soon die. If it drops further down 5 volts, it is time to bring around a new one.

Next, when the engine starts to run, the alternator will produce a current, and the battery reading will begin to rise again. The reading will return to a higher value of around 14 volts in an ideal condition. (1)

Anywhere outside this range indicates either an under-charged or over-charged battery. Hence, the alternator must be looked into, or it’ll ruin your car’s battery.

How to Test Battery with Multimeter

What Are the Symptoms of a Bad Car Battery?

You might face the following issues that point toward a busted battery:

  • Low battery level on the dashboard display
  • Clicking the engine when the car is turned on
  • The need for frequent jump starts
  • Delayed ignition
  • Headlights won’t turn on, are dim, and won’t sustain running for 2 minutes.

How Long Should a Car Battery Last?

Most car batteries have a warranty of four years, but they might not last that long. They tend to function for 3-4 years before needing to be replaced with a new one.

When Can I Not Use a Multimeter to Test a Car Battery?

If you do not have maintenance-free batteries, you can use a hydrometer to test such car batteries. If you want to identify them, maintenance-free batteries have plastic caps on every cell. (2)

Final Verdict

You do not need professional help to perform the above steps, and testing a battery with a multimeter is one of the easiest and cheapest ways.

References

(1) alternator – https://auto.howstuffworks.com/alternator1.htm
(2) hydrometer – https://www.thoughtco.com/definition-of-hydrometer-605226

Video Reference

ChrisFix

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About Sam Orlovsky

b1d87d2ee85af3e51479df87928bdc88?s=90&d=mm&r=gCertifications: B.E.E.
Education: University Of Denver - Electric Engineering
Lives In: Denver Colorado

Electrical engineering is my passion, and I’ve been in the industry for over 20 years. This gives me a unique ability to give you expert home improvement and DIY recommendations. I’m not only an electrician, but I also like machinery and anything to do with carpentry. One of my career paths started as a general handyman, so I also have a lot of experience with home improvement I love to share.

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