How To Test a Car Battery
Dealing with dim headlights? Weird electrical gremlins? Here’s how to check if your battery is the culprit.
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The reality is that like almost every component under the hood, a car battery has a finite lifespan and will conk out on you eventually. Weather conditions, corrosion, electrical shorts, charging issues, and other factors can speed up the process. Just as there are a number of ways a bad battery can manifest itself in your car—weird electrical problems, trouble starting, dim headlights, a bulging case, and more—there are a number of ways to test a car battery to make sure it's functioning correctly.
The easiest is to use a multimeter or a load tester, but you can do it without tools as well. But honestly, every garage should have a multimeter. Anybody can pick up a decent one for less than $40, and it can be used to test all types of electrical connections on your car. Battery? Test it. Relay? Test it. Alternator? Test it!
Whichever route you choose, the process of testing a battery is very simple, even if you've never even heard of a multimeter before. Besides, it's better to learn a new skill than wait for your battery to die and leave you stranded at the most inconvenient time.
Everything You'll Need to Test a Car Battery
Testing a car battery is an easy project that should take 10 minutes to complete, and you can do it anywhere you have a safe parking spot. However, for your first time you'll want to move slowly and carefully—though this is a very safe process, batteries are heavy, there's always a risk of electrical shock if you're not careful, and dying or dead batteries can be dangerous if they're leaking fluid.
Safety First
Tools and Parts
- Multimeter and/or battery load tester
- Ratcheting socket set
- Battery charger (optional)
As we mentioned, a battery can also be tested without tools, but we'll start with the most exact method.
How To Test a Car Battery
Multimeters and battery load testers are two different tools with the same goal: measuring the voltage coming out of your battery. The difference is that a multimeter is designed to measure the battery's resistance, voltage, and current while putting as little load as possible on it, versus a battery load tester being designed to measure the current under a specific load.
Using a Multimeter
- Pop the hood, locate the battery, and move any terminal caps out of the way.
- Clean the terminals, if necessary.
- Turn on your multimeter and turn it to DC voltage, then 20 volts.
- Touch the black probe (negative) onto the negative (black) terminal.
- Touch the red probe (positive) onto the positive (red) terminal.
- View the reading on your multimeter display. A healthy battery should read out between 12.5 and 12.8 volts.
Using a Battery Load Tester
- Make sure the battery is as charged as possible, then pop the hood, locate the battery, and move any terminal caps out of the way.
- Remove the battery cables using your ratchet.
- Clean the terminals, if necessary.
- Mate the positive load tester clamp to the positive terminal, they will be red.
- Mate the negative load tester clamp to the negative terminal, they will be black.
- Press the load test switch and leave it on for about 10 seconds.
- If the tester reads 9.5 volts or lower, your battery is bad and needs to be replaced.
Multimeters are pretty cheap tools that are definitely worth owning, but if you haven’t gotten around to it yet, there are other ways to check your battery’s health.
Auto Parts Stores
Most nationwide auto parts stores, such as AutoZone or Advanced Auto Parts, offer free services for battery testing and charging. If you’re able to drive your vehicle there, it’s a great resource.
The Headlight Test
This is an unscientifically imperfect way to test your battery, but it can be an easy method for checking its health.
- Turn the headlights on for five to 10 minutes without turning the car on.
- Turn the car on.
- If you notice your lights significantly dim down when the car is turned on, your battery doesn’t have the right charge and might be on the way out.
Testing a Car Battery FAQs
Q: Can you jump start a dead battery?
A: Assuming there is nothing wrong with the battery, it should start. However, during a time when a battery is not used, there are all sorts of issues that could arise, including corrosion that could damage the battery and cause it to short. If you have a bad battery, you wont be able to jump it, but if it’s just low on charge, it should work.
Q: Can a bad alternator ruin a new battery?
A: If an alternator is bad, it’s possible that it could either undercharge the battery and allow it to die, or overcharge the battery and ruin it.
Q: How do you clean battery terminals?
A: You’ll need a wire brush and some baking soda. We've got you covered with our guide to cleaning battery terminals.
