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Q: How Do I Check the Voltage of My Car Battery?

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How do I check the voltage of my car battery?

You can get a general idea as to whether your battery is suspect by the voltmeter gauge in your car if it has one. These gauges are not too accurate as they are marked in wide increments and are really intended to be an indicator of the condition of your car’s charging system. However, if the gauge indicates less than 12 volts when just turning the key to the "on" position (do not crank), your battery’s voltage is probably too low to crank your engine.

A more accurate way to check the voltage is with a digital multimeter. These instruments can read not only DC and AC voltage, but also amperage and resistance. They are fairly inexpensive at most auto parts stores and home centers.

Safety goggles are always a good idea when checking the voltage of your car. First, find your battery, which may be located under the hood, in the trunk, or possibly under a seat inside the vehicle. Make sure that there is nothing electrical turned on in your car which will draw power from your battery. The multimeter uses 2 lead probes, one black and one red. The black lead plugs into the common or "com" jack & the red lead plugs into voltage, also known as "volts" or "V", jack. On the rotator switch of the multimeter, select DC volts. Take the red probe & touch it firmly to the "+" terminal on your battery. Take the black probe & touch it firmly to the "-" terminal on your battery. You will get a digital voltage readout to the hundredths scale (xx.xx). A sufficient voltage to crank your engine is 12.45 volts or higher. Any reading less will probably not crank your engine enough or at all. A fully charged battery will measure 12.66 volts or higher.

This test will give you the voltage of your battery at the time you actually test it. It will not indicate whether or not your battery can hold the present voltage. To get an idea as to whether your battery is still good enough to hold a charge you need to recheck the voltage after several hours. A good battery will not show an appreciable drop in voltage when you take this second reading. If you have a substantially lower reading, your battery needs replacement.

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