How To Test A Car Battery With A Multimeter

Testing car batteries with digital multimeter.

There are times when your car seems to have a hard time starting, or some electrical components fail to work as expected. You have a suspicion that the battery is at fault, but you are not sure of it. In these instances, knowledge of how to use a multimeter to test a car battery will come in handy.

Testing a battery to learn if they are fully charged, undercharged, or faulty is one of the easiest ways to troubleshoot problems with your car. The battery is responsible for a lot of electric components like the radio and the power windows, not to mention that it gives the required electric jolt to get the engine up and running. Provided you have the correct tools at your disposal, checking the battery will be a very easy but fulfilling task.

Safety First!

Before you attempt to take any of the steps given in this guide, please make sure that you are wearing all the proper protective gear. These include gloves for your hands, goggles for your eyes, and other articles of clothing that will protect your skin.

This is because batteries have materials that are corrosive and they may damage your skin or your eyesight should the substances accidentally spill on you. Wearing insulating gear is also a must, so that you will not be at risk of accidental electrocution.

Ways To Test The Battery

There is more than on method to test that status of a car battery, but one the true tried and tested ways is by using a multimeter. When you have all this tool and the protective gear ready and at your disposal, then you can proceed with testing the battery’s charge first.

1. Locate The battery

The first step, of course, is to locate where the battery is situated in your car. You can consult the manual for this if the auto manufacturer put the battery in some weird, obscure place. But you usually can find the battery just under the car’s hood, not far away from the fender.

2. Set Up Equipment

After you have located your battery and worn the proper protective gear, you can then set up your equipment for the test. Turn off the headlights and the engine ignition, and then remove the protector caps covering the battery’s terminals, if there are any. This is also a good time to clean those terminals up, if they exhibit signs of corrosion.

Batteries and multimeters usually employ color coding to indicate the polarity of each terminal. Red usually means positive and black usually means negative. If this is the case, then you should connect each mulitimeter lead wire to its corresponding terminal.

It should be noted that there is usually no serious result if you put the wrong lead in a terminal (i.e. putting the positive or red multimeter lead in the negative of black terminal)— this usually just results in a negative (or inverted) reading.

However, to be on the safe side, you are of course reminded that the correct lead should be attached to their corresponding terminals.

3. Measure The Charge State And Read The Results

Now that you got your equipment set up, all that is left is to turn on the multimeter and set it to DC volts mode. AC setting is used with household appliances like refrigerators or washing machines, and DC is what we need to test the car battery.

If the reading is anywhere between 12.4 to 12.7 volts, it means that the battery is sufficiently charged (75 percent to 100 percent charged). If the result is anything below 12.4 means that your battery needs to be charged.

The actual table of values is as follows:

12.66 volts = 100% charged

12.45 volts = 75% charged

12.24 volts = 50% charged

12.06 volts = 25% charged

11.89 volts = 0% charged

Note that these values are based on a temperature of 80 degrees Fahrenheit. Battery voltage will change at around 0.01 volts for every 10 degrees of change upwards or downwards this base temperature.

Also be reminded that at this stage, we have not figured out if the battery is bad or needs replacement yet. We just figure out its charge state. Of course, a battery in a low state of charge may still be good; it just needs to be recharged.

Likewise, a battery that is fully charged but cannot hold said charge for a reasonable time may be considered bad. A good battery is one that can be hold a charge consistently.

4. Charging Your battery

If you find that your battery is below full charge, you must charge it to full before performing further tests. A portable car battery charger will do wonders in this state of charging, but using the car’s alternator would not hurt, either. Seeing as the battery is below optimal charge, you might need to jump your battery in order to use the alternator to charge it.

After this, you will need to drive the car for about 20 minutes at the speed of around 40 miles per hour or greater. This will give the battery the charge it needs. Alternatively, you can just remove a battery and get it charged at an auto repair store. You may have to pay for this service, but some shops do it for free.

5. Further Tests

Once the battery is fully charged, you can now perform additional tests with it. There are several ways to go around this.

One is by using a load tester to determine if the battery can hold a charge. In this method, load is applied to the battery while testers monitor the status of the battery. If the voltage drops below 9.6 volts when the load is applied during the test, you can consider the battery as bad and it should be replaced. (Find the best car brands where you can purchase).

Another test is to use an electronic tester. This method sends a frequency wave to the battery so that the condition of the energy cells inside can be determined. Both of the above methods can be performed at an auto repair store. Some ask for payment for the service, while other shops are willing to do the tests for free.

However, there is one quick test you can perform with an assistant to determine the state of the battery, and this is by “cranking” the engine. Cranking the engine involves turning on the ignition and holding the key in position for 2 seconds. The key is to get an assistant to crank the engine while you monitor the battery’s voltage during the process.

The basic principle is the same as load testing: if the voltage drops to below 9.6 volts during the process, it means that the battery is bad and needs to be replaced. When the voltage drops below this number, it likely means that the battery is sulfated and cannot hold or accept electrical charge.

Checking For Leaks

Sometimes, a battery’s inability to hold a charge is not the only problem. A combination of acid and dirt deposits can build up on the battery cover as well, which may lead to an energy leak. Fortunately, there is a simple way to check for leaks, but you also need a multimeter for this. First, you must set the multimeter to a low voltage setting.

After turning the multimeter on, touch the deposits that build up on the negative terminal of the battery with the device’s negative (black) probe or lead. If the device registers even a bit of voltage from the deposit, it means that leakage has begun in the buildup and you might have to clean the battery.

However, if there is zero voltage from the reading, but you still think there is a drain going on somewhere, you may check for a parasitic drain. This means that there is a different circuit responsible for the drain, and you have to identify the circuit by isolating it from the battery system.

The Multimeter

Having tool to check the voltage. We have talked about testing with a multimeter extensively in this article. But those new to the world of auto repair may be wondering what multimeters actually are.

A multimeter is an instrument that measures multiple electrical values like voltage, current, and resistance. There are analog multimeters, which employ a needle that goes back and forth to indicate the measurement, while digital ones show the numbers on a digital display.

Digital ones tend to be more accurate and precise, but analog types still has its uses. For example, when measuring a value with rapid variations, the analog’s needle can make it easier to interpret the fluctuations.

Multimeters cost anywhere from US$10 for the cheap models to US$5,000 for the high end brands with certified calibration.

Conclusion

You now know everything that you essentially have to know about how you should test a car battery with a multimeter. The steps contained herein present a general approach, and is applicable to a wide variety of battery and car models, with only slight variations in each case.

Hopefully, this will give you confidence to perform your own tests on batteries you suspect are failing and may need replacement.

Hi, I am Mark Neal From San Francisco in the United States. I’m the founder of BATTERY MAN GUIDE since last December in 2017. My team from Philippines  and i have been working very hard to write lot of articles about “product reviews” and “how to guide” on batteries we believe they will help for what you look for! You may sometimes find some incorrect grammars and less engagement dialogue but we will improve our contents continuously along the way. To be honest, we are still not well established battery website, but we are trying to become an authority in this industry in the future by providing valuable information for our readers. With that being said, thank you for visiting at BATTERY MAN GUIDE and we are looking forward to having a great relationship with you!