How to Test a Car Battery With a Multi-Meter
If your car won't start, and the headlights are dim or do not come on at all, you need to check your battery. A multi-meter, also called a digital voltmeter, can be used to check and test electrical components such as your car battery. It is easy to use, and a tool that you should keep on hand to check your battery from time to time.
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Instructions
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How to Use a Multi-Meter to Test a Car Battery
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Open the hood of your car and locate your battery. Look for the positive (+) terminal on the battery. Remove the protective cover to the positive terminal.
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Connect the positive (+) red lead on the multi-meter to the positive (+) terminal on your car battery.
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Connect the negative (-) black lead on the multi-meter to the negative (-) terminal on your car battery.
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Leave the multi-meter connected to the car battery overnight. Do not try to start or run the car. Check the reading on the multi-meter in the morning. If the car battery is functioning, the voltage on the multi-meter should read between 12.5 and 12.8 volts. If it reads less than 12.5, you need to charge your battery.
Checking a Car Battery with a Multi-Meter After it's Been Charged
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Connect the multi-meter to the battery terminals with the car running. Connect the positive lead on the meter to the positive terminal on the battery; and the negative lead on the multi-meter to the negative terminal on the battery.
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Check to see if the charged battery is registering at 13.5 to 14.5 volts or more. If it is less than 13.5 volts, the alternator is not producing enough current to charge the battery. In this case, have the alternator tested at an auto repair shop; you may need to replace your alternator rather than your battery.
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Have the alternator tested at an auto repair shop; you may need to replace your alternator rather than your battery.
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Tips & Warnings
When testing a battery, use these guidelines:
12.68 volts = 100 percent charge
12.24 volts = 50 percent charge
11.89 volts = no charge
Readings are based on an outside temperature of 80 degrees Fahrenheit. Voltage readings drop about .01 volt for every ten degrees F. So when it's 30 degrees Fahrenheit, a 100-percent charged battery will read at 12.63 volts on a multi-meter.
