How to Test a Car Battery With a Multimeter

You think your car battery might be low on juice and you'd like to use your multimeter to see if it is really low. Testing a car battery with a multimeter is easy if you know what settings to use and where to connect the leads. Here are the easy steps in testing your car battery with a multimeter.

Difficulty: Moderately Easy

Instructions

1. Open up your hood and locate your car's battery. Be sure to follow the manufacturer's directions and properly disconnect the cables from the battery.

2. Turn your multimeter off, then set your multimeter to 50 volt scale. This will reset the meter and give a more accurate reading.

3. Connect the red lead to the positive battery terminal. Be sure to put the lead on the post of the battery and not just on the cable to get the most accurate voltage reading.

4. Attach the black multimeter lead to the negative battery terminal. Again, be sure to put the lead directly on the post of the battery for the most accurate reading.

5. Read your multimeter gauge after 15 seconds. If it has a digital readout and you have a 12 volt battery, it should read at least 9.6 volts running through the multimeter for it to take a charge. If it's less than that, you need a new battery.

Tips & Warnings

• Check the temperature if your car battery testing is showing lower than 9.6 volts. At lower temperatures, the minimum voltage under load goes down as well. For instance, at 30 degrees F, the minimum voltage is only 9.1 volts.

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[techarry]

on 9/9/2009 Re: "That’s a bogus test for a bad battery."
The article doesn't suggest testing with the engine running. The 9.4 volts was meant as a threshold to determine if the battery is even worth keeping in the car. A reading of 10.5 volts or less usually indicates a shorted cell. A fully charged 12v car battery should test 12.4 - 12.7 volts with the engine off. A conventional lead-acid battery is considered fully charged at 12.7 volts. Maintaining at least 12.4 volts makes the battery last longer by preventing buildup of sulfur on the lead plates. When the car is running, the meter should read around 14.4 volts to indicate that the alternator is working properly.

[WyattEarpFan]

on 10/1/2008 I have a battery that goes drains for some odd reason. I recharge it then its ok for a whole month. Then starts to drain. I have a multi meter but I have no idea what or how to check what might be draining the battery. It looks like a fairly good batter, maybe 1 year old or so more. Do you know batteryguy??

[bettercarguy]

on 7/29/2008 That’s a bogus test for a bad battery. If it is running and only has 9.6 at the battery its time to test the charging system. 9.6 volts is what most ignition systems take to operate, leaving nothing to run lights, radio, wipers etc.. To properly test a battery it needs to be charged to 75% (12.4 ) and then tested under a load.