How to Charge a Car Battery

The battery in your car may not be the fanciest part of your vehicle, but it’s undoubtedly one of the most important. Car batteries play a huge role in keeping your car running well. When your car is turned off, and you want to use the electrical features, like the stereo or the headlights, it’s your battery that powers them. But most importantly, your battery is what powers your car starter when you turn it on. When you turn your keys, the battery sends power to the starter motor, which cranks the engine and gets things started. Without a properly-charged battery, you won’t be able to fire up the engine.

Batteries can lose their charge for a number of reasons. The most popular culprit is when you simply drain the battery by leaving the lights, or some other electrical component, turned on. If that happens, you’ll need to charge the battery.

How a Battery is Designed

Duralast batteries in a line at the shop.

Car batteries are designed very similar to household batteries, with a positive electrode, a negative electrode, an electrolyte, and a separator. The electrodes, known as the anode and the cathode, are highly conductive, which allows energy to pass between them. Power comes into the battery through the anode (the negative end), and out through the cathode (the positive end).

On the outside of the battery, both the positive and negative terminals are placed on top, or at the top of one side, of the battery, as this design allows you to easily access both terminals without removing the battery from the car. As such, you can easily charge a car battery while it is still under the hood.

What Charging a Battery Does Inside

The process of charging a battery is fairly simple. Electrical charge enters the battery from an outside source, typically the alternator when the engine is running, which activates a chemical reaction inside the battery. That chemical reaction is converted into electrical energy, which is stored inside the battery’s cells. 

Steps to Properly Charge a Battery 

Normally your car’s battery is charged by the alternator. When your car is running, the alternator is the main source of electrical power. Most of the electrical features, like the stereo, headlights, interior lights, and power windows, are powered by the alternator. In addition to powering those electrical components, the alternator sends power to the battery to charge it. That way your battery should be fully charged when you turn your car off, and thus capable of doing its job and getting your car turned back on when you next use it. 

However, if your car battery isn’t charged enough to turn the car on, then you certainly can’t rely on the alternator to charge the battery, because alternators only run when the engine is running. When that happens, you’ll have to charge the battery yourself. There are two main ways to do this.

Using a Battery Charger

The first is the traditional way: by using a battery charger

  • With all of the electronics in the car turned off, disconnect the negative battery cable, then disconnect the positive battery cable. 
  • Make sure that the cables are not resting near each other, as you don’t want them touching. 
  • You’ll probably need a socket wrench when disconnecting the cables. 
  • Next, clean the battery terminals using a battery brush or a battery cleaning solution. 
  • Now it’s time to use your battery charger. Different chargers might have different instructions, so read through the manual first, but in general, they all work pretty much the same. 
  • With the charger turned off, connect the positive cable from the charger to the battery’s positive terminal, then do the same with the negative cable and negative terminal. 
  • Then turn the battery charger on, and it will begin the process of charging the battery. 
  • Once the charging is complete, turn off the charger and remove the cables from the battery terminals. 
  • Reconnect the car’s battery cables, and again be sure to do the positive cable first, and the negative cable second. Then you’re good to go.

Jump Start the Car

A woman with jumper cables preparing to show how to jump start the battery in her jeep wrangler with a Chevy van

The other way to charge a battery is by jump-starting your car. To do this, you’ll need a pair of jumper cables and a second car, or you’ll need a portable jump starter

If using another car, park that car with the hood near your car’s battery. Clamp one end of the red jumper cables to the positive terminal on the dead battery, then clamp the other end to the positive terminal on the working battery. Then clamp one end of the black cable to the negative terminal on the working battery, and clamp the other end to a metal bracket on the car with the dead battery. Turn on the car with the working battery, then turn on the car with the dead battery. Once the car is running, disconnect the negative cables followed by the positive cables. 

If using a portable jump starter, the process is essentially the same, but without a second car. Instead, you’ll just have to press a button, then turn on your car. 

Once your car is running, you’ll need to run it for at least 15 to 30 minutes so that the alternator has time to charge the battery. If you just turn your car off as soon as you jump-start it, it probably won’t turn back on. 

How Long Does it Take to Charge a Battery? 

It depends entirely on how powerful your charger is, and how dead the battery is. In general, it usually takes around 12 hours to fully charge a car battery with a charger at a slow and steady rate. If you’re jumping the car, it usually is instantaneous to get the car running, and then takes 30 minutes of running the vehicle before the battery is mostly charged. 

If you need to buy a battery, battery charger, jumper cables, or any other tools, you can find them from all of the top brands at AutoZone. At AutoZone, all orders come with Same-Day In-Store or Curbside Pickup, and Free Next-Day Delivery is available on eligible orders. 

If the job is too big for you, seek out one of our Preferred Shops to help you do the job.

Advice, how-to guides, and car care information featured on 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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