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How to Charge a Car Battery

One car jump-starting another.

You turn the key (or push the button) and . . . nothing. Your battery is dead. Perhaps it’s time for a new one, but not necessarily. Here we’ll discuss how to charge a car battery to help you save some time and money when the need arises.

How Long Has It Been?How to charge a car battery

The first question you’ll need to answer is “how old is my car battery?” If it’s four years or older, you should probably buy a new one. Even the best batteries only last so long, and past that point, they simply won’t hold a good charge.

That number can even be lower (more like two or three years) if you live in a place that gets very hot, as extreme temperatures kill car batteries faster.

If fast drainage is a chronic problem for your vehicle, a battery defect may be the cause of the issue. Again, replacement is your best bet. But if your battery is new enough and usually functions properly, you may be able to bring it back to life.

Check Your Charge

Take a voltmeter and see what you’re dealing with. A healthy battery will give you a reading of 12.4 to 12.7 volts across both terminals. If the voltage is well below this, the battery will have trouble turning the crank to start the engine. You’ll want to hit this range before you try to start the car again.

If your battery charge doesn’t approach this number or it drops quickly from it even after the following fixes, you’ll likely be making a trip to the store for a replacement.

Option One (12 Volts or Above): Jump It and Drive It

Assuming there’s no problem beyond a temporary discharge from lack of use or leaving a light on, this is number one on the list of how to charge a car battery. Jump-start the vehicle with another vehicle or a portable jump-starter, and then drive it at speed for half an hour or so before you turn off the engine. Your alternator, a small generator that uses the engine’s motion to create an electrical charge, will top off the battery while you drive.

Try to keep power-leeching features like air conditioning and infotainment off while your alternator is recharging the battery. Ideally, you’ll want to drive your vehicle in daylight while this is happening so that you’re not using the headlights. Drive it again in the next day or two to make sure the charge has held. Oftentimes, that’s all you need to do, and it’ll be months or years before you find yourself with a problem again.

Option Two (Less Than 12 Volts): Charge It Where It Sits

You can damage your alternator if you try to charge a battery with too low of a voltage reading, so your best move in that case is to use a dedicated battery charger. A good charger is a wise investment that can keep your vehicle charged during periods of little use, and it can revive your battery if the charge does get too low to start the car. Modern battery chargers are smart and use a series of programs to test, charge, re-test and shut down your battery to tend to it without causing damage or wasting electricity.

Make a habit of monitoring and maintaining your battery’s health so you don’t hear that dreaded click-click-click when you really need to get somewhere quickly.

Check out all the batteries and battery accessories available on NAPA Online, or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on how to charge a car battery, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

Photo courtesy of Wikimedia Commons.

Mike Hagerty View All

Mike Hagerty is an automotive journalist whose work has been featured on radio, TV, in print and online since 1997. He's the Publisher and Editor of MikeHagertyCars.com, and contributes car reviews to the Los Altos Town Crier and losaltosonline.com. Previous outlets have included KFBK and KFBK.com in Sacramento, California, the ABC television affiliates and Hearst-Argyle and Emmis radio stations in Phoenix, Arizona; AAA magazines for Arizona, Oklahoma, Northwest Ohio, South Dakota and the Mountain West and BBCCars.com.

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