How To Test A Car Battery

how to test a car batteryTesting your car battery is easy. All you need is a battery load tester and a digital volt meter. 

Here’s how to test a car battery.






Testing The State of Charge

Here’s how to test a car battery using an hydrometer.

First, clean the battery and make sure there is no obvious physical damage or bulging of the sides. Replace the battery if damage is observed.

If you have cell caps that can be easily removed, remove them and check to see if each cell is filled to the bottom of the battery top, like in the photo below.

replace a car battery

If not you can fill them with distilled water. Be careful not to over fill.  Fill them only to the bottom of the battery top, not all the way to the top. You can use battery hydrometer, like the one in this photo, to determine the specific gravity of each cell in the battery.


Each cell should read within .050 from your highest reading to the lowest reading.  If not, put the battery on a [easyazon_link asin=”B000NCG7QQ” locale=”US” new_window=”default” tag=”carbattery0e-20″ add_to_cart=”default” cloaking=”default” localization=”default” nofollow=”default” popups=”default”]battery charger.[/easyazon_link]

Most battery chargers will have a red and green scale indicating the charge of the battery. Continue to charge the battery until the charger is in the green part of the scale.

Battery Charger

After charging, use the hydrometer to see if all cells are within .050 of the highest reading to the lowest reading.  You need at least a charge of 75% for the next test.

If you have a hydrometer reading of 1.217 or higher, and a voltage reading of 12.4 or higher you have a good charge on the battery.  At this point, you can load test the battery.


Test With a Load Tester

Here’s how to test a car battery using a load tester.

You have to first remove the “surface charge” of the battery.

The surface charge is simply a 12 volt or more voltage reading that remains on the battery after it is charged.

This can give you a false reading of 12 volts when the battery is actually reading lower.

Simply hook up your load tester to your battery and press the test button for a few seconds. Another way if you have not removed the battery from the car, is to just start the car and immediately turn the engine off. Do this twice.

If the voltage reading is below 12 volts it is likely that that the battery will not charge up and is no longer usable.

load TesterIf the battery holds a charge, you can apply a load test by pressing the test button. A load test of 10 seconds should be enough to get a good or bad reading on the tester.

Technically, you should be able to apply a load of half the cold cranking amp rating of the battery for 15 seconds and the battery voltage should not drop below 9.5 volts.

With most small testers, like the one on the left, all that is necessary is to load the battery for 10 seconds and observe the needle.  It will read good, weak, or bad.

While applying the load test take your digital volt meter and take a voltage reading.  Any reading below 9.5 volts is indicating a weakened battery.

Dead Car Battery

Ideally, after removing the surface charge, and while load testing for 10 seconds, you should expect to see a voltage reading of  9.5 volts or more.

But any reading below, you should replace the battery.

At this point, hopefully you have a healthy battery that has passed all the tests.

If you have one that has failed the test, check the following in addition to replacing the battery for good measure.


Points To Keep In Mind 

I hope you found this information on how to test a car battery useful.  Please leave a comment or question below.



Thanks For Visiting!

Edward Verheyden

Edward Verheyden is the founder of  He has a 30+ year mechanical background and is the main reviewer here.  He lives in San Diego CA with is wife and two daughters.


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  • anna says:

    I’ve never had the need to test a car battery before, but I feel like with this set of tips, I could probably do it! 🙂 Thanks for sharing to a rookie car gal.

    • eddie says:

      You’re Welcome. I hope these pages will at least give people background knowledge the next time they’re car is in the shop!

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