How To Charge A Car Battery

Whether you take your car maintenance seriously or haven’t been for a tune-up in a while, most drivers will encounter a dead battery at some point. Calling a roadside maintenance service, like AAA, or figuring out how to get your vehicle to a repair shop can be both timely and costly, and is not the perfect solution for everyone.

You can avoid wasting time and money by learning how to charge your own car battery with the following steps.

Disclaimer: Working with car batteries poses risks such as electric shock and potential damage to vehicle systems if improperly handled. Please use caution while attempting any vehicle maintenance and always consult your car manufacturer’s manual.

The first step in learning how to charge a car battery is prepping it to be charged. You’ll need to determine whether or not your car’s battery needs to be removed from its holding tray or if it can be charged as is.

Technically all automotive batteries can be charged while still connected, but it doesn’t hurt to do a quick clean of your car’s battery prior to charging it.

Turn Off Car Electronics

After preparing your vehicle’s battery for a battery charge, you’ll need to turn off your car engine. Then, turn off your vehicle’s entire electrical system, including any interior lights. Confirm that all power is off before progressing to the next step of the charging process.

It is absolutely necessary that you first remove the negative cable and then the positive cable from your battery’s terminals in that order. Otherwise, you may cause an electrical short or damage your car’s battery.

The negative cable is almost always a black cable with a “-” symbol present. The positive cable is typically a red cable with a “+” symbol. To remove each cable, you may first have to remove the plastic caps that are sometimes located on car battery terminals.

For most car batteries, you need to use a 10.0-millimeter socket wrench to loosen the negative cable, while being careful to keep it away from the positive cable as a charge could transfer between the two sources. Finally, repeat the process with the positive cable and terminal while still taking care to keep the two cables separate.

Before charging your car battery, it’s important to clean out your vehicle’s battery terminals. We recommend using a terminal cleaning brush, which is similar to a toothbrush in both shape and appearance. A terminal cleaning brush is used to clean battery terminals by clearing away corrosive debris and chemicals.

A terminal cleaning brush is best paired with a commercial battery cleaning solution, but a mixture of baking soda and water will be just as effective at neutralizing battery acid, preventing corrosion, and thwarting any possible malfunctions. We recommend a ratio of one cup of distilled water to one tablespoon of baking soda.

If you’ve completed the steps above, you’re now ready to connect the car battery charger to your vehicle’s battery. The following instructions will work for most car battery chargers, but if your charger has specific instructions for operation, follow those instead.

• Ensure the car battery charger is turned off.
• Connect the positive cable to the positive terminal first, then connect the negative cable to the negative terminal in that order.
• Turn your car charger on and set the charge rate to the lowest possible setting.
• If your charging system has a timer, set it for the appropriate time period. If your charger doesn’t come equipped with a timer and you’re unsure of how long to charge your car battery, consult your owner’s manual or search online to prevent potential overcharging.

Removing The Car Battery Charger

To complete the car battery charging process, power off your charger before you touch anything else. Once your car charger is turned off, simply disconnect the positive cable first, followed by the negative cable.

Remember to replace the cables on the terminals of your car battery. Once again, be sure to reconnect the positive cable before the negative one. If you removed the car battery entirely, now is the time to set it back in its tray.

To properly test your car battery, you shouldn’t drive your car for a couple of days after charging. This is because your car’s alternator charges the battery while your vehicle is running. However, this part of the process is not absolutely necessary, as we understand many drivers need their cars on a day-to-day basis.

If you do decide to test your car’s battery, we recommend using an automotive multimeter and following these steps:

1. Connect the battery tester. Attach the red cable to the battery’s positive terminal and the black cable to the negative terminal. Then turn on the automotive multimeter.
2. Test battery voltage. To do this, you should be aware of the fact that most car batteries are 12.0 volts. A fully charged battery should show 12.6 volts or higher, while 12.4 volts will start your car and 12.0 volts or lower requires additional charging. You can use a voltmeter for this step, but you will need a multimeter later in this process.
3. Test cold cranking amps. Cold cranking amps (CCA) help show the health of your car battery. Each car battery features a CCA rating, which can be tested using a multimeter’s CCA mode to compare against the battery’s CCA rating.
4. Perform a cranking test. After setting your multimeter to cranking test mode, you’ll need to start the vehicle. Then your device should display the lowest voltage that your car battery is able to maintain while the starter is working. Healthy batteries typically maintain between 9.0 and 10.0 volts.
5. Perform a charging test. Last and certainly not least, switch your multimeter to charge testing mode while your vehicle is still running. Healthy car batteries usually read between 14.2 and 14.5 volts. Anything below this range indicates your alternator or part of your car’s charging system needs to be checked out.

Our team also recommends using a battery maintainer to keep your car battery fully charged. These clever devices can be left on and attached to a car battery without fear of overcharging.

Car batteries are finicky pieces of equipment but are absolutely essential as they’re the main power source to make your car run and drive. Even if you purchase a new car, it’s simply luck of the draw whether or not you get a bad battery. Knowing how to DIY and charge a car battery will provide you with the knowledge to get back on the road with just enough power to get home or a full charge for the weeks of driving ahead.

We asked Zac Salerno, a technician at Import Performance, what car owners should consider in order to get the maximum life out of their vehicle batteries.

“If you’re going to be gone for a while, have someone start your car for you if the car’s not going to get started for a couple of weeks,” he said. “I start all my cars once a week if they have their motors together [and assembled]. It’s always good to keep the batteries going because they will die if they just sit.”

“If you disconnect the negative terminal, the battery life will be elongated,” he continued. “But for the most part, as long as you’re driving your car, just double-check the terminals to make sure they’re not super corroded. Just take a toothbrush [and] clean them off real quick. Maybe get some terminal grease or dielectric. Just rub it on there and it’ll be fine for the most part.”

There are two types of battery chargers: standard car battery chargers and trickle chargers. If you’re unsure of where to start looking for products, check out some of our helpful guides where we have performed hands-on testing to ensure the quality of each recommendation.

“Trickle chargers, like the Battery Tender and the Tender Junior – always worth it,” said Kyle Marker, Parts Manager at Leith Lincoln and self-proclaimed DIY car mechanic. “You ask me why? It’s because my Mustang won’t start right now because I [haven’t started] it in three weeks and the battery had 3.6 volts.” A trickle charger, though, would get the job done.

To ensure the accuracy of all the tips and information in this guide, we consulted our network of experts for their thoughts on car batteries. These experts have over 100 years of combined experience in the auto industry, in fields ranging from detailing to accessories to tires, and everything in between. Interviewing experts ensures that all the information and advice we publish is as accurate as possible and delivered in a way that’s helpful and easy to understand.

Our team then combed through dozens of resources such as federal safety studies, research from reputable institutions, verified firsthand accounts, interviews and videos from credible automotive professionals, and our own prior testing conducted by our expert testing team.

Why You Can Trust Us

Since 2020, we have published over 200 auto product reviews in an effort to make owning a car and shopping for auto products easier. Our team of writers, editors, researchers, and product experts collaborates to thoroughly vet everything we publish. We try to perform in-house testing on real vehicles whenever possible before making our buying and informational guides.

When testing is not feasible, however, our aim is to make your life easier by doing all the online research for you. For more information on our testing methodology, check out our methodology page here.

*Data accurate at time of publication.