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Auto Electrical

How to Quickly Test Your Car Battery to See If It’s Faulty

If you think that your car’s battery is faulty, here is a simple test you can do which will reveal if it is or not. You only need a simple multimeter (and possibly a friend) to complete this test.

  1. Grab your multimeter, and if it’s not autoranging, set it to 20V DC.
    How to set your multimeter to test your car battery
  2. Turn off the ignition and any accessories that are still on, like lights, radio etc.
  3. Take the red lead of the multimeter and put it on the positive post of the battery
    Placing positive lead on positive battery post
  4. Take the black lead of the multimeter and put it on the negative post of the battery.
    Placing negative lead on the negative battery post
  5. Now see what the multimeter says. If it is showing anything below 12.4 volts, your battery could be faulty or needs to be charged.
    Multimeter reading of your car battery

If the battery has consistently been getting flat and it’s showing less than 12.4v on the test above, then odds are it needs to be replaced.

One further test you can do is a cranking test:

  1. Follow steps 1&2 above, then disable your vehicles ignition or fuel system (a quick way to do this is to full the fuel pump fuse out). This will allow the vehicle to crank without firing, which is what we need.
  2. Place the leads of the multimeter on the battery posts like before, red on positive and black on negative.
  3. Have your friend/helper to crank the car – for no longer the 15 seconds – and see what the multimeter says. If the voltage drops below 9.6 volts, you’ve got a weak battery on your hands.

One last quick tip. If you are seeing a negative reading on your multimeter (such as -12.6v), it means you have connected the multimeter leads the wrong way round to the battery. Don’t worry, this won’t cause any problems, it will just show you a negative reading.

If you’ve performed these tests and find you have a weak battery, give us a call now on 09 218 7789 and we will be able to sort you out a quality replacement for an excellent price.