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Test a car battery

How test a car battery

Do a search and you’ll find lots of posts about how to test a car battery with a voltmeter. Those tests will tell you the state of charge of your battery at that moment in time. But a voltmeter alone can’t tell you the battery’s condition or give you any kind of prediction of remaining life. For that, you need a digital battery tester.

What does a digital battery tester do?

To use a battery tester, you first enter the cold cranking amp (CCA) specification listed on the battery’s label. Then you press the start button. The tester will first check the voltage. Then it will conduct a simulated load test, which used to be the gold standard of testing. Then it will conduct an internal resistance test, and finally a conductance test.

What is a battery load test?

A battery load test is basically a stress test for the battery. The tester loads the battery to 1/2 of its CCA rating for 15-seconds. The voltage must remain above 9.6-volts during the test for it to succeed. Like the voltmeter test, this test tells you the battery’s condition at that time, but doesn’t give you any idea of internal resistance. So it can’t be used to predict battery life.

What does an internal resistance test tell you?

As the battery ages and the lead plates deteriorate and form sulfate crystals, internal resistance between the plates and main bus increases. Increased resistance is an indicator of remaining battery life. In other words, high internal resistance is a sign of internal deterioration. Most digital car battery testers report the results in terms of pass/fail rather than Ωs.

Examples of digital battery testers

Midtronics is considered top-of-the-line in the auto trade. But their products are pricey. Expect to pay at least $200 for a Midtronics battery tester. A less expensive and equally as accurate is the Solar BA9 battery tester (around $55 on amazon).

midtronics battery tester

Midtronics battery tester

solar battery tester

Solar BA9 battery tester

Battery testers to avoid

Several companies make a combination of volt and load tester. In the industry, these are referred to as battery toasters because the load test uses heating coils similar to those used in a toaster. They’re cheap, but not very reliable because the resistance of the coils changes based on their temperature. Perform the test and you’ll get one reading. Perform it 15 seconds from now and you’ll get a different reading.

dead car battery

“Toaster” style battery tester

battery tester

Old fashioned battery tester

If you don’t own a digital battery tester, see this post on how to test your car battery with a voltmeter.

©, 2020 Rick Muscoplat

Posted on by Rick Muscoplat


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