How to Change a Car Battery

man installing car battery — Replacing a car battery on your own is a fairly easy procedure. Natalia Kokhanova/Shutterstock

Car batteries have an uncanny ability to die at the most inconvenient times. If it's pouring down rain on a cold night when you're on your way to an important event, the chances of your car battery going kaput hover near the 100 percent mark. This is why humans invented roadside assistance.

First, though, it's a good idea to see if your battery needs to be replaced or if it simply could use a good cleaning. Sulfate, created over time by the battery's discharge of lead, can build up on the terminals as a cakey white substance that prevents the battery from recharging during use. You can get rid of this sulfate with a simple solution of baking soda and water [source: AAA].

Here's how to use it: First, be sure the car is turned off and brush the solution onto the sulfate to loosen the deposit. After the terminals are clean, try the ignition. If the car starts up, it should be able to recharge itself and you may not need a replacement after all. A jumpstart may also be necessary to give it enough juice to turn the engine again.

If your battery is fully dead, consider having a professional do the job for you. Batteries can be heavy: The average car battery weighs between 25 and 40 pounds (11 and 18 kilograms). It may be even heavier in large vehicles like diesel trucks. Most auto parts stores offer free battery installation when you purchase a new one from them.

At this point, you've decided your battery must be replaced and that you're going to handle it yourself. Good for you. Read on find out what tools you'll need to do the job correctly.

Tools Needed to Change a Car Battery

You want to fix your car battery yourself, but don't jump the gun just yet. Get the proper tools together before going under your car's hood.

If you've already created the baking soda and water solution you need to clean your terminals, keep it handy. You'll want to give the terminal cables a more thorough cleaning. If not, then go ahead and whip up a batch and drop a clean paintbrush into it for later.

Break out your toolbox and select a few of the tools you'll need. The battery terminal cables are held fast around the battery terminals by nuts and bolts. This means you'll need a crescent wrench, an adjustable wrench, vise pliers or a socket wrench. Most battery terminals will come with either 10 mm or 12 mm (0.4 or 0.5 inches) socket-sizes. Grab another pair of adjustable pliers to hold the bolt head in place as well.

It may sound funny, but you'll also want to bring a hammer with you. A gentle tap or two can help loosen a stubborn terminal cable from the terminal post.

It's also a good idea to invest in a battery terminal cleaner. This handy and inexpensive tool is designed to brush away corrosion from the terminal posts and the end clamp of the cables. It also primes the posts of your new battery for a better connection to the terminal cables. If you have a good narrow metal wire brush, that can do the trick as well. While you're picking up a terminal cleaner, spring for a can of corrosion protector, which will help prevent corrosive sulfate buildup in the future.

Lastly, bring along a pair of sturdy gloves and safety goggles. Batteries can be dangerous, (as we'll see in the next pages) and protecting your hands and eyes is a good idea. Also keep some rags or cloth handy to wipe up mess, and a plastic container to organize your tools.

Got everything together? Good. It's time to go outside again.

Preparing Your Car for a Battery Change

First and foremost in preparing your car for a battery change is ensuring that the battery isn't receiving any power from your engine. You may have found that your battery needs replacing after it failed to turn over, so your keys may still be in the ignition. If so, remove them. Without the keys, your car's electrical system shouldn't be active, which will reduce the chance of a spark or shock while you're changing your battery.

If you've already brushed on the baking soda and water solution to the terminals, you're ahead of the game. If not, go ahead and clean the terminals as fully as possible. Removing the sulfate deposits should make it easier to unscrew the nuts from the bolts on the cable ends and from the posts. Gently knock the posts and cables with your hammer to break up the deposit. Then brush on the baking soda solution and finally wipe it away with a rag.

Once the battery is cleaned, inspect it for cracks where acid might escape when you remove it. Make a mental note of these places so you can avoid placing your hands near them during removal. You might also want to place duct tape over any cracked areas to provide a layer of protection — albeit a minimal one.

Lay your tool container on the ground or position it in the engine bay. Just be sure not to place it on a hot surface where it can melt. Avoid a metal toolbox, as it could potentially contact the battery and spark.

Your battery is cleaned, you've searched for cracks and your tools are laid out. It's time to remove your old battery.

Removing Old Car Batteries

battery termials — Remember that the red terminal is positive while the black (or uncapped) one is negative. Jsnow my wolrd/Shutterstock

Finally, we get to the good part: removing the old battery. Remember that this is the most dangerous stage in the replacement process. Cracks and corrosion in the old battery can allow acid to leak out onto your skin, which can be unpleasant to say the least. While the car's ignition is off, the battery can still produce an electrical charge (and even an explosion) while the terminals are connected. If a metal wrench contacts both battery posts at the same time, it can short circuit and lead to shocking or burning hazards. Be careful about removing the battery, and only touch one post at a time.

To start, loosen the nut from the bolt that holds the terminal cable to the negative post on the battery. Remember that black is the negative terminal and red is the positive one. Use your wrench or pliers to turn the nut in a counterclockwise direction. You don't have to take nut and bolt off entirely, just enough to get the terminals off.
Hold the bolt head in place using another pair of pliers or wrench. Once loose, carefully slide the end clamp from the post, and position in such a way that it won't slide back onto the battery top. When you do, be sure you have already placed your tools on the ground or on your Styrofoam tray to prevent sparking an electrical charge.
Once the cable connected to the negative terminal post has been safely removed, follow the same steps for the positive terminal. The red terminal usually has a small cap you can pry back.
Now that both terminals are loose, it's time to unfasten any plate that holds the battery in its seat. Most likely, you'll encounter the same sized nut as the ones found on the terminal cable clamp or a wing nut you can unscrew by hand. Once it's loose, you can now safely remove the battery. Remember, it can be heavy, and you'll likely be hunched over it; be sure to lift with your knees.
Lift it straight up — most batteries come with a handle attached for easy carrying — and then out and onto the ground. If the handle has corroded, carefully lift the battery by its sides. Be careful not to allow any acid to spill out.
With the battery safely away from the car, use your battery terminal cleaner to brush out any remaining sulfate from inside the terminal cable end clamps.
Check the cables to make sure they're not corroded. If they are, pick up some replacement cables at the auto parts store.
Apply a coating of corrosion protection spray to the cable end clamps to protect from future deposits from accumulating on your new battery.

Now you're ready for the last step, installing the new battery.

Attaching New Car Batteries

installing new battery — New batteries can be very heavy. Joe Belanger/Shutterstock

Congratulations, you've reached the home stretch. Just a couple more steps and your car should purr like a kitten once more on the first turn of the ignition.

Lift the new battery and place it into its seat under the hood. By now, you've likely concluded that new batteries are much heavier than old batteries; be careful when lifting.
Your new battery may have come with colored plastic caps on the terminal posts. Don't remove them until you've situated the battery and are ready to attach the terminal cables. These caps will help you remember which post is positive (the red one) and which is negative (the black one).
Once it's situated firmly in its seat, begin the reverse of the operation you undertook to remove the old battery. Start with the positive terminal. Remove the plastic cap and use your battery terminal cleaner to brush the new posts. This will score the metal lightly, which will provide a better grip between the posts and the clamps, which provides easier recharging of your battery while you drive.
Spray another coat of corrosion protection on the terminal post.
Slide the end clamp over the post until it sits against the bottom of the post. Using your pliers or wrenches, hold the bolt head steady while you tighten the nut in a clockwise direction. Repeat the same steps for the negative terminal.
With both terminals attached, refasten any plate or support that holds your battery in place. While the design of this feature is sometimes a little tricky, don't skip this step. The plates hold the battery in place as your car jostles over rough terrain and speed bumps. Driving with an unattached battery is a bad idea.
At this point, try your car's ignition. It should start right up if your battery was the root of your car's trouble. Since the battery was unattached, you may have lost information in your car's onboard computer. This might require you to re-enter a password for your radio and other features to operate once more.

There's one last step you'll need to take to complete your jaunt into the world of do-it-yourself automotive repair — disposing of the battery. The combination of lead and acid in car batteries make them toxic waste, so you'll have to take it to the proper recycling center or to a service station, where they'll be disposed of for a fee. The store where you bought your new battery might be required to take your old one, depending on what state you live in. Just don't throw it away. Most car batteries are recycled into new ones, preventing toxic contamination of the environment.

Lots More Information

Sources

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