How To Test Your Car Battery With A Multimeter

multimeter car battery

Many motorists learn that their battery needs to be replaced too late, and wind up stranded in a cold parking lot or worse.

Fortunately, there’s a simple tool that indicates when you need to replace your car battery. Here’s how to test it with a multimeter.



What a multimeter does

A multimeter measures volts, amps or resistance from an electrical source. The instrument fits in the palm of your hand with a digital or analog display and two probes connected with cables. You can purchase low-end multimeters for less than $20.



Using a multimeter to test your battery

Multimeters have a variety of household uses. Here’s how to use one to test your car battery:


  • Prepare the battery. Open the hood and locate the battery. The positive terminal is red with a plus sign (+), and the negative terminal is black with a minus sign (-). Check the terminals for green/grey ash buildup and remove any corrosion with a wire brush or sandpaper.


  • Set the multimeter. Don’t be intimidated by all the settings because the general idea is simple. Turn your multimeter dial to the 20-volts setting. Touch the red probe to the red terminal and the black probe to the black terminal.


  • Measure the battery at rest. A battery at rest with the ignition turned off should show a voltage reading between 12.2 and 12.6 volts. Anything lower than 12.2 volts means your battery isn’t fully charged and is in danger of dying.


  • Measure the battery when starting and idling. Testing your battery when turning the ignition will show you its strength when it’s under the most draw. You’ll need a second person to start your car while you hold the probes.


If the reading falls to less than 10 volts while your ignition is being turned, the battery is weak and you may need tojumpstart your carsoon. A strong battery cranks out between 14 and 14.5 volts. A reading below 14 volts means your battery is weak or your alternator is failing.



  • Test the alternator. The alternator generates electricity for your car’s electrical components and charges your battery while the vehicle is running. While idling, turn on the car’s headlights, stereo and air conditioner. If the multimeter displays less than 13.5 volts, then your alternator is struggling to charge the battery and you should consider replacing it.

 

Car batteries in Toronto, Winnipeg, Brandon, Regina and Edmonton


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