A bad battery will leave you stranded more quickly and thoroughly than many other more severe car problems. Unfortunately, there's not much you can do to fix a dead battery other than replacing it with a new one. Even jump-starting is often a temporary solution and may leave you stranded again before you can make it home.
However, batteries aren't cheap, and you want to be sure you need a replacement before spending that cash. Testing your battery is the best way to decide on your next step. Fortunately, you have plenty of options for checking the condition of your charging system. This guide will discuss three approaches to battery testing so you can decide which one is best for your situation.
1. Resting Voltage Test
If you have a multimeter on hand, you can perform a quick and easy test to check your battery's condition. Testing your battery with a multimeter won't be as reliable as using professional tools, but it can give you a good head start before moving on. If your multimeter test indicates a problem, it may still be good to have a professional check the battery before replacing it.
To test a battery with a basic multimeter, set it to DC voltage and touch the negative probe to the negative terminal and the positive probe to the positive terminal. You want to see a value of around 12.6V with the car turned off. Anything significantly lower than this can potentially indicate an issue with your car's charging system.
2. Alternator/Charging System Test
There's more to testing a battery than just checking the voltage with the car turned off. If you can start your vehicle, recheck the voltage with the engine running. The alternator charges the battery while the car runs, so you should see a reading on your multimeter higher than the resting voltage with the car turned off.
Your alternator should generate at least 13.5V while running, so you should see a similar (or higher) value from your battery. A lower reading indicates a charging system issue, although it doesn't necessarily point to a failing battery. In this case, you'll want to perform further diagnostics to rule out problems with the battery, alternator, and other elements of your car's charging hardware.
3. Load Testing
Load testing is a more thorough way to test the condition of your battery and requires specialized equipment. You can usually bring your battery (or your whole car) to a local mechanic or an auto parts store for a free or low-cost load test. A load test will confirm any issues with your battery, at which point it's a good idea to replace it as soon as you can.
However, don't ignore the issue if your battery passes a load test. Low voltage readings on either of the tests above indicate a charging system issue. While a good battery load test can rule your battery out as the culprit, you'll still need to determine the underlying cause of the problem.