How to Change a Car Battery

Knowing how to change a battery, and change it correctly, can extricate you from situations like the following:

Your battery dies late at night, perhaps in your own driveway or miles from home. You find a filling station that will sell you a replacement, but the station attendant tells you the mechanic will not be available until morning. You can install it yourself or wait until the mechanic j shows up for work.

Or, at a winter resort, you attempt to start your car after leaving it out all night in the cold, but the car won't start, and you have an appointment four hours away back at the office. The resort will loan you a battery, but you will have to install it.

Or, your car battery, which has already received one recent boost, shows signs of continued weakness. You have a dozen appointments and simply don't trust the battery to get you where you're going and home again. Until you find time to have a new battery installed, you have to borrow the battery from your wife's car.

Changing a battery isn't difficult if you don't mind a bit of dirt and grime.

What To Do

1. With a wrench, disconnect the battery's negative cable, which is clamped to the battery's negative terminal post. The negative post is identified by a minus symbol (-) or the abbreviation NEG.

2. If the battery also has a negative ground wire (a few batteries do), disconnect it using a screwdriver or a wrench. A ground wire is usually attached to the engine.

3. Disconnect the positive cable from the positive battery post. It's labeled with a plus sign (+) or the abbreviation Pos.

4. Remove the battery cable clamps. This can be difficult when a battery is old and its terminal posts and clamps are corroded or bonded by rust to one another. To remove a clamp, first loosen its bolt and nut. They hold and squeeze the clamp in close electrical contact with its post.

Whereas some batteries have dispensed with bolt and clamp post-fasteners, many still use them. The bolt usually has two square-headed nuts. One is part of the bolt (stationary); the other is threaded to the bolt. Often you need two holding tools to remove them: an adjustable wrench and vise-type grip pliers.

Lock the bolt head with pliers and use the wrench to loosen and unscrew the threaded bolt. Or switch tool positions, if that's easier and gives you a better grip.

Even with the bolt and its nut loosened, you may have to pry the clamp from the terminal post. In prying, you don't want to put any pressure on the battery terminal itself. Doing so can easily crack the battery case or punch a hole right through it. To pry the clamps from their posts, use a screwdriver to force apart the clamp's jaws. As you pry open the jaws, work the clamp back and forth on its post, loosening the bond between them. If a clamp won't slip upward and off its post, squirt the post and clamp with a lubricant.

5. With the cables and their clamps freed from the posts, remove the battery and put it aside.

6. Set the replacement battery in position (on the tray where the old battery was) and lubricate its posts. You can use any handy lubricant, including grease, petroleum jelly, or even motor oil. A lubricant eases the clamps more easily over their battery posts and postpones corrosion.
If you're installing an old or used battery, before reinstalling the clamps and before applying a lubricant, clean each post to remove corrosion or rust. Any handy abrasive will scour them clean, enhancing electrical contact with the clamps. A slurry of baking soda and water usually does the job. So will sandpaper. Even a little sand mixed with radiator water, both probably readily available wherever the emergency occurs, are credible battery terminal cleaners. Use a toothbrush or a rag to apply your abrasive. With the old posts clean, lubricate them before reinstalling their clamps.

If you're installing a new battery, its terminal posts should already be clean and corrosion-free. It will need no special attention other than application of a lubricant.

7. Now slip the positive cable clamp over the battery's positive terminal post; next install the negative clamp and its negative cable on the negative post. If the battery also has a negative ground cable, reattach it to the engine or wherever it was connected.

8. Finally, retighten the clamp bolts and their nuts. They've got to be as tight as possible to ensure good electrical contact.