It never fails - you’re in a rush and the kids are throwing a tantrum in the backseat. You go to start your car and all you hear is a clicking sound. Great.
You think the battery is your problem but you’re not sure. Fortunately, you can check the state of charge of your battery using an inexpensive multimeter. This test will reveal whether or not your battery is fully charged.
Part 1 of 2: Test the battery
In order to safely and efficiently test your battery, you need a couple of basic tools.
- Safety glasses
- Protective gloves
- Digital multimeter
Step 1: Find the battery. The first step is to locate the battery.
Most batteries are under the hood near the fender. However, some manufacturers like to hide the battery in obscure places. They could be in the trunk, under the back seat - and some are even mounted in the wheel well!
If you can’t find your battery, consult your owner’s manual or do a quick search on your car model to reveal the location.
Step 2: Set up your test equipment. Turn the vehicle’s lights and ignition off, and have your materials ready.
Touch the black multimeter lead to the negative battery cable and the red lead to the positive battery cable. No need to panic if you get the leads backwards; you’ll just see a negative reading instead of a positive one. This is just a gentle reminder that the red goes to red and black goes to black.
Turn your meter to the DC volts setting. This is the DC reading with the line above it. The DC reading with the squiggly thing (sine wave in technical terms) is AC voltage. This is not the setting you want, unless you plan on testing household appliances. So, save AC for the washing machine.
Step 3: Read the test results. Check the voltage reading on your screen.
Battery voltage readings are as follows:
- 12.66 volts = 100% charged
- 12.45 volts = 75% charged
- 12.24 volts = 50% charged
- 12.06 volts = 25% charged
- 11.89 volts = 0% charged
These readings are for a battery at 80 degrees Fahrenheit. Battery voltage will change .01 volts for every 10 degree change in temperature.
Step 4: Interpret the results. If your battery is greater than 12.45 volts it is sufficiently charged. Anything below that should be recharged and tested with professional test equipment.
- Note: A state of charge test does not indicate whether your battery is good or bad. It only indicates the current state of charge. A battery that has a low state of charge may still be good after it is recharged. A good battery is one that will hold a charge. A bad battery is one that will not.
Step 5: Charge your battery. If your battery has a low state of charge, the next step it to recharge it and test it further.
This can be done with a portable battery charger, or by charging your battery with the alternator. If you decide on the second option, you will need to jump your battery first. Then, drive the vehicle for 20 minutes or so at speeds greater than 40 mph. You can also remove your battery and have it charged at the auto parts store. Most will perform this service for free.
Step 6: Fully test the battery. Once the battery is fully charged, it can be tested to determine whether it is good or bad. Most auto parts stores will do this for free.
There are two methods for fully testing a battery:
With a load tester: This test applies a load to the battery while the tester monitors the battery voltage. If the voltage drops below 9.6 volts during the test, it is bad and should be replaced.
With an electronic tester: This test sends a frequency wave through the battery to determine the condition of the cells inside.
That’s it! Testing a battery is relatively simply, inexpensive and leaves you with a sense of empowerment. So, next your car won’t start and you suspect a dead battery, whip out your multimeter and get to work. If you prefer to have a professional test your battery, give the team at YourMechanic a call.
This article originally appeared on YourMechanic.com as How to Check a Car Battery and was authored by Mia Bevacqua.