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How to Charge a Car Battery

One car jump-starting another.

It is bound to happen at some point in your motoring life. You hop in the driver’s seat, turn the key (or push the button) and . . . nothing happens. 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?” Check the purchase date sticker on the battery to find out when it was put into service.  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 starter to crank 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 More): Jump 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. This is basically how to charge a car battery without a charger.

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.

How To Use A Car Battery Charger

Charging a car battery is easy. Here’s how to charge a car battery at home using a plug-in battery charger. Make sure to read the instructions that come with your battery charger so you can take full advantage of any features and understand how it operates. If possible provide ventilation in the charging area to help disperse any hydrogen gas which may be generated during the process.

  1. Clean the battery terminals of any corrosion or gunk to allow for a good connection with the charger.
  2. Connect the battery charger clamps to the car battery (positive side first, then negative).
  3. Turn on the battery charger.
  4. Select the charging amperage (if applicable). Lower amp charging takes longer, but is easier on the battery.
  5. Let the battery charge pausing every 30 minutes to check the battery voltage with a multi meter. If your battery charger is equipped with an automatic cutoff, simply let the charger operate until it shuts itself off. This lets the charger itself decide how long to charge a car battery with no guessing
  6. Once the battery is fully charged simply remove the battery charger clamps and put away the charger.

Figuring out how long does it take to charge a car battery depends on the capacity of the battery, the charge left in the battery,  and the charging amperage.  Answering how long to charge a dead car battery could mean an hour or as long as overnight, assuming the battery is not completely done for and can still take a charge.

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. If you are ever in doubt just swing by your local NAPA AutoCare and have your battery tested.

Check out all the vehicle batteries and battery parts available on NAPAOnline, 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 or how to charge a dead 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, and contributes car reviews to the Los Altos Town Crier and Previous outlets have included KFBK and 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

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