How To Test a Car Battery

“Do I need to replace my car battery?”

How can you tell if your car battery just needs to be recharged, or if it needs to be replaced? Sometimes you can recharge a car battery and it’ll last you another 50,000 miles, but sometimes, it’ll just leave you stranded again 50 miles later. “Do I need to replace my battery?” I asked myself,  while staring at a car that was so dead my key fob wouldn’t even unlock the door. Time to find out. Here’s how to test a car battery.

I had accidentally killed my car battery twice in a month, in the dead of Canadian winter. The weather alone was cold enough to kill a car battery. Having left some lights on, and the heated seat on while the engine was off, definitely didn’t help. There was also the fact that I bought my car second hand, so I had no idea how old it’s battery is.

While we typically only do motorcycle content, I thought, what the heck, this will only take a minute, so I’ll show you guys the two ways I test a car battery.

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How to test a car battery

What you’ll need

Here are my recommendations for testing a car battery yourself:

• Ctek battery charger (you can use these on both car and motorcycle batteries)
• Multimeter (works for both automotive and home electrical)
• Battery load tester (works on everything from car and motorcycle to trailer and winch batteries)

Before testing a car battery, make sure you charge it!

The first thing you’re going to do in order to test your car battery is recharge the battery and make sure it’s fully charged. A weak battery will most likely fail the test, even if your battery could still be in good condition. The battery needs to be fully charged in order to be tested fairly.

To recharge your car battery, you can get a battery tender like this one from Ctek. The reason why I love it (I own a Ctek 3300), is because I can use it on both my motorcycles as well as my cars.

Motorcycle batteries are very small, and car batteries are very big. A car charger will burn a little motorcycle battery because the car charger is too powerful. At the same time, a motorcycle battery charger will take forever to charge a car battery because the motorcycle charger is too little. The Ctek is a great charger because you can switch between car mode and motorcycle mode, so no matter what kind of vehicle you’re charging, you can do so safely and quickly.

After you’re done charging the battery, disconnect the charger, and let the car sit for an hour or so, so that the battery can go back to whatever it’s “normal” resting voltage level is.

Method #1: Use a multimeter to test the car battery voltage

Get a multimeter, even this cheap $10 multimeter is perfect for the job. Multimeters are great because you can use them for everything from your car, motorcycle, and trailer, to home electrical, they’re dirt cheap, and they last a lifetime.

Set the multimeter to 20 volts, and then connect the red cable to the positive battery post, and the black cable to the negative battery post. The multimeter will tell you what the battery’s resting voltage is.

If the battery at rest (not being charged for some time) is under 12.6 volts, you should replace your battery or you run the risk of your battery leaving you stranded again.

Method #2: Use a battery load tester to test your car battery’s performance

A battery load tester only costs about $25 to $32, and like the multimeter, it’ll last forever. You can use a load tester on anything from a car and motorcycle, to a ride on lawn mower, camping trailer, antique car, or anything that uses a 12 volt or even 6 volt battery.

The load tester works by drawing a controlled load from your battery, and then monitoring how the battery performs under pressure to determine whether or not the battery is still good or needs to be replaced.

Using a load tester is easy, you simply clamp red to red and black to black, and then you hold the button for no more than ten seconds and you watch the indicator, which will show Green (Good), Weak, Bad. I tend to replace batteries if they show anything other than Good. Even a weak battery will leave you stranded sooner than later, so it’s better to play it safe. If your battery tests Green/Good, you don’t have to replace it.

Note: Unlike a multimeter test, using a load tester will put some strain on your car battery. That’s why even if your car battery passes the load test, you should still put the battery back on your Ctek charger one more time.

Conclusion

For only $100, or less than the cost of a battery you might not need, you can have all the tools to easily charge and test your car battery yourself from home. Compared to having to get your car towed, taking it to a mechanic, or “playing it safe” and buying a car battery that you might not need, having the tools in your own garage to test your battery yourself is a no-brainer financial decision.

The process is pretty simple to how to test a motorcycle battery. Of course, if you are looking for information on motorcycle batteries, you might also want to learn about how to fill, seal, charge, and install a brand new motorcycle battery. Luckily, when it comes to car batteries, most big chain retailers will already have this done for you.

If you have any questions on how to test your car battery, leave me a comment down below. Hey, if you just found this content helpful and want to leave a comment letting me know it worked for you, I’d appreciate that too. Don’t forget to subscribe to my YouTube channel here, or to my email list (right sidebar) for more maintenance tips and tricks.