How To Test a Car Battery With a Multimeter
You get in the car and turn the ignition but don't hear the comforting hum of your engine. It won't start and the lack of power indicates it's probably the battery. Sometimes the reason is obvious, such as realizing you left your headlights on all night. But other than searching "how to tell if car battery is dead," how do you know if you can jump it or just need to replace it? A cheap tool and a simple test can let you know if your battery is holding a charge. Learn the easy solutions to potential problems that can come with a busted battery.
Testing Your Battery
Using a multimeter, you can determine if your battery is healthy enough to keep around. If it is, you can often recharge it to make sure it runs well in the future. If not, it's time to purchase a new battery in a local store or online.
If you don't have a maintenance-free battery you can use a hydrometer.
Testing Batteries with a Multimeter
Before you learn how to test a car battery, there are a couple of things to keep in mind. First, a multimeter only works on maintenance-free batteries (the kind without plastic caps on the individual cells.) The other type must be tested with a hydrometer. Second, you should only test a battery after it's been sitting unused for at least an hour. If you test it immediately after use, you can receive a false reading from a unit charged by your car's electrical system. Once you're sure you can use your multimeter, you're ready to get started.
Test Your Battery
How to Test a Car Battery With a Multimeter
Prepare Your Multimeter
Set your multimeter to voltage and ensure it's adjusted to 20 DC volts.
Touch the Probes to Your Battery Terminals
Press each probe to the correct terminal, touching negative to negative and positive to positive. Your multimeter and battery are probably both color coded, so the negative terminal and probe will be black while the positive terminal and probe are red.
Turn on the Headlights
Activate the battery by having someone turn on your vehicle's headlights.
Check the reading
Once the vehicle is on, check the multimeter. It's a good idea to write down the reading. Then, compare it to the voltage figures below.
The temperature outside affects the voltage of the battery. At about 80 degrees, a fully charged battery will be around 12.5-12.6 volts. To be more specific: a fully charged battery ideally measures at 12.66 volts and above, but 12.6 volts at 80 degrees, 12.588 degrees at 30 degrees, and 12,516 volts at 0 degrees are acceptable readings. A 75% charged battery will measure closer to 12.45 volts while anything below 12 volts indicates the battery is effectively discharged.
If you get a reading between 12.3 and 12.5 volts, try charging the battery up to full. Don’t hook it up to the car overnight and re-test it in the morning. If battery that holds a charge that indicates a problem on your vehicle that is draining the battery. A good place to start is to check the alternator. You can either do that yourself or bring your alternator to your local AutoZone for free testing.
Advice, how-to guides, and car care information featured on AutoZone.com and AutoZone Advice & How-To’s are presented as helpful resources for general maintenance and automotive repairs from a general perspective only and should be used at your own risk. Information is accurate and true to the best of AutoZone’s knowledge, however, there may be omissions, errors or mistakes.
Be sure to consult your owner’s manual, a repair guide, an AutoZoner at a store near you, or a licensed, professional mechanic for vehicle-specific repair information. Refer to the service manual for specific diagnostic, repair and tool information for your particular vehicle. Always chock your wheels prior to lifting a vehicle. Always disconnect the negative battery cable before servicing an electrical application on the vehicle to protect its electrical circuits in the event that a wire is accidentally pierced or grounded. Use caution when working with automotive batteries. Sulfuric acid is caustic and can burn clothing and skin or cause blindness. Always wear gloves and safety glasses and other personal protection equipment, and work in a well-ventilated area. Should electrolyte get on your body or clothing, neutralize it immediately with a solution of baking soda and water. Do not wear ties or loose clothing when working on your vehicle.
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