How to reconnect a car battery? Step by step guide

We are going to tell you a little secret: changing a car battery does not require special tools, and it is also available to anyone. You don’t have to make great efforts, and unless you do it in the August sun, you shouldn’t even sweat. Without. more, we explain how to change a car battery.


The first step to change the battery is … Sure: find it. In the vast majority of cars, it is located in one corner of the engine bay. Whether in the front, behind one of the headlights, or in the back, just below the windshield, on either side. Keep in mind that it could be hidden under a plastic cover, especially if you drive a car made in the last decade. Don’t panic if you don’t see her under the hood; Some automakers (like BMW ) often prefer to install the battery under the back seat or in the trunk, to save space. Your owner’s manual will help you find it, if you are not sure of its location.

You found it? Well, now is the time to roll up your sleeves. Speaking of which, we recommend wearing clothes that you don’t mind getting a little dirty. Ah! And make sure you know the code for your car radio. In some cars, disconnecting the battery resets the stereo and a permission code will be requested the next time you start it.


Your 12-volt battery has a positive and a negative terminal, just like the AA batteries you used to put in your Game Boy Color. It is connected to the car’s electrical system through metal terminals. Find the two ends of the terminals (remember that the positive part may be under a plastic cover) and note how they are secured. You’re in luck if your car has a quick release clamp. Otherwise, you will need a wrench to loosen the ends of the terminal. Bolt size varies from car to car. Some use 10mm bolts, some others 13mm and others use one each. You could even find a car with a 7mm bolt. or a completely different size.

Start by disconnecting the negative end of the terminal. It is the one with a symbol  next to it, usually on the battery case. The bolt should not require a lot of effort to loosen. Make sure your key never touches both terminals at the same time. Doing so will cause sparks to fly, and this is the last thing you want to see while working on a gasoline engine. Gently pull up on the terminal end once it is loose to remove it, and get it out of the way. Do the same for the positive terminal, this time making sure the key doesn’t touch any metal parts of the car (like the hood).


Both terminals are disconnected from the battery, now what? You can’t just take out the battery. It is usually held in place by a retention system that generally consists of a strap or metal plate. Either way, you’ll need a socket wrench and extension bar long enough to reach the bolt.

Loosen slowly and make sure not to loosen the bolt. We recommend using a telescopic magnet to retrieve it before it falls and is lost in a dark, greasy chasm, also known as the engine compartment. You can also use a pair of pliers, or simply reach down and grab it, if you have enough room to do so.


Now, you are ready to remove the battery. It is relatively heavy, and can reach 20 pounds or more, depending on its size, so be prepared. Look at the ends of the terminals before reinstalling the new one. If you see a buildup of green, gray, or white dust, you’ll need to clean them with cloth or sandpaper to keep the charging system in great shape. Don’t wear anything too thick. Sand the inside of the terminals until they are nice and shiny. Battery acid is corrosive, so you should wear gloves and try not to let anything fall on your clothes.


Put the new battery in and don’t forget to tighten the retention system you removed earlier. Most new batteries come with anti-corrosion and grease washers to keep terminals free of dirt. Remove it and then connect the positive terminal of the battery first, always making sure that the key does not come into contact with another metal part. It must be tight, unable to move the end of the terminal by hand. But don’t squeeze it too tight, or you’ll break it. Repeat these steps for the negative end.

Double check (or three times) that you have not left any tools in the engine compartment. Close the hood and start the car to make sure everything works as it should.

Congratulations! You just changed your car battery.

Leave a Reply

Your email address will not be published. Required fields are marked *