Rick's Free Auto Repair Advice

How to test a car battery

Test a car battery

I have lots of other cool car battery posts on this site
How to clean car battery terminals and posts
How a car battery works
How to replace a car battery cable terminal
How to charge a car battery
What are cold cranking amps?
Who makes the best car battery?
What is car battery reserve capacity? 

Use a voltmeter to test a car battery

You can use a voltmeter to test a car battery. It’s not the most accurate test, but it can tell you the current status of your battery. I’ll show you how to use a voltmeter to test your battery below. BUT, the test results cannot be used to determine the condition of your battery going forward. For that you need a real battery tester that conducts a simulated load, capacitance and resistance test. I’ll get into those towards the end of this post

How to test a car battery voltage with a voltmeter

Set your voltmeter dial to DC volts >12 or 15. Attach the red lead to the positive (+) car battery terminal and touch the black lead to the negative (-) car battery terminal. At 70° a fully charged battery will read around 12.6 volts. For other temperatures, see the chart below.

If the battery test at or above the stated voltage, that does NOT, by itself, mean the battery is good. All you’ve done at this point is to confirm the battery can maintain voltage. The voltage test does not confirm car battery amperage capacity. In other words, a battery can output proper voltage but may not be outputting enough amps.

Use a voltmeter to test a car battery capacity

Now we’re going to use the same setup to test the car battery’s ability to output amps. Leave the meter hooked up and have a friend start the engine. The voltmeter will dip during cranking and then bounce back up to a near normal reading. This happens quickly. If the meter shows voltage dipping to less than 10-volts during cranking, the battery is in poor condition and should be replaced.

Why a digital battery tester is more accurate

A solid state battery tester like the Solar BA9 is a great way to test the overall condition of your battery. This tester checks several types of batteries, from the traditional flooded lead acid (SLA) found in most cars, to Absorbed Glass Mat (AGM) flat plate, AGM spiral wound and even gel cell batteries used on electric start lawn mowers.

The tester conducts a simulated load test, conductance and resistance test. When a car battery tests good using this type of charger, it’s an indication that you can count on the battery to perform into the future. Repeat the battery test each season for peace of mind


©, 2018 Rick Muscoplat

Posted on by Rick Muscoplat

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