Replacing the battery in your car is a task that most anyone who is even a little handy with tools can accomplish. But remember that a battery is an energy storage device and any such device is capable of causing damage if it releases all of its energy at once so pay attention to the safety warnings below.

A car battery consists of a plastic case containing thin plates made of lead and other metals. The case is filled with sulfuric acid that covers the plates and causes a chemical reaction that produces electricity. The battery has two round metal cylinders that protrude from the top or side. These are the “posts” and provide the attachment points for the battery cables that carry the electricity to the engine. One of these posts will be marked with a positive (+) sign and the other with a negative (-) sign. Usually the cable attached to the positive terminal will be colored red while the negative cable will be black. However it not a good idea to trust this color coding since mechanics sometimes will use a black cable on the positive or vice-versa. Trust the markings on the battery case and double check by verifying that the negative (-) cable is attached directly to the engine or chassis.

Here’s the SAFETY WARNING. When working on a battery, never allow any conductive material, a metal wrench, a piece of wire or a metal sheet (including the cars hood, etc.) to touch both posts of the battery at once. Doing so creates a short circuit condition that will cause the battery to explode spraying chunks of lead, plastic and sulfuric acid all over whatever happens to be nearby. This can cause serious injury and even death. Also, don’t smoke or have any open flames near a battery. Batteries release hydrogen gas which is extremely flammable. Work on the battery is a well ventilated area.

Let’s begin the replacement process. First, examine the battery and cables. An accumulation of white or yellowish-white powder on the posts indicates corrosion caused by the battery acid reacting with the metal of the posts. You can clean this away with a cloth but use a cloth that can be discarded since the acid will destroy it. Remember the orientation of the battery since the new battery must go in exactly the same way.

The next step is to disconnect the negative battery cable from the battery. It is important to do the negative cable first. Some cables have clamps that go around the upright battery posts while others have bolts that screw directly into the post. Corrosion may have eaten away at the bolts so you may have to use pliers or vise grips instead of a wrench. Fasten the cable out of the way so it can’t fall back and hit the battery or you then repeat the procedure for the positive cable.

The battery is held in by a strap across the top or side or by a small clamp near the bottom of the battery. Remove the bolts securing the clamps and the battery should be ready for removal. Again corrosion on the bolts may be a problem and be careful of short circuits caused by the straps touching the posts.

Wiggle the battery around to make sure it is free of the clamps and lift it out of the car. Batteries are heavy so have a good grip and a clear space to set it down quickly. The outside of the battery may have acid residue on it so don’t let it touch your clothes or skin. Wear gloves if possible and wash your hands as soon as possible.

Now inspect the battery compartment. If corrosion exists you can clean it with water in which you have dissolved some baking soda. If the battery cables are badly corroded you might want to replace them. Once the cleanup is complete, install the new battery by performing the removal steps in reverse. To prevent corrosion, you can coat the posts and other exposed metal with Vaseline or bearing grease. Auto parts stores also have spray-on coatings for this purpose. Since most batteries come precharged, you should now be ready to turn the key and drive on.