1) Before you start
Before working on your car’s battery, take off all jewelry and don’t wear clothing with metal zippers. Shorting out your battery with something metal will create sparks, massive amounts of heat and could spark an explosion of hydrogen gases that may have formed in the area of the battery.
If that freaks you out, stop reading right now and head to your local mechanic.
Still here? OK, let’s begin.
What you’ll need:
- A wrench suitable to remove the terminals; a wrench, perhaps, to remove the battery hold-down posts
- A jar of petroleum jelly
- Two felt battery-post pads (if it’s a top-post battery)
And, of course, the replacement battery.
The fasteners for the battery clamps can often be prone to rounding, so try to not use an adjustable wrench. Use instead a fixed wrench that fits well. If bolts are already rounded a bit, use locking pliers to get a firm grip.
2) Remove the old battery
The first thing to do, of course, is remove the faulty battery. If at this point you can see the negative cable — a heavy cable that runs from the battery to a point on the chassis or engine — disconnect that from the battery now. If the posts are covered, proceed to the next step, but as soon as you can see the negative post, disconnect it. Safety first.
Then, see if the battery is held down by a pair of posts typically midway along either long side of the battery. These are typically shaped like the letter ‘J’ and are hooked at the bottom support plate and held in place by nuts at the top holding down a strap across the battery. Some carmakers use a rubber bungee-like strap, others use a plastic shroud held down by the same kind of posts described above.
Now, disconnect the positive cable and remove the battery.
Recycle the old battery
And don’t forget to recycle the old one. Some places including Advance Auto Parts will accept your old battery, and even provide an incentive.
3) Installing the new battery
Before moving forward, here’s the entire process in a quick 3-minute video:
Once the old battery is out, inspect the cables. If you see signs of broken strands of the wires or frayed insulation presenting the possibility of a short, replace the connector or the cable. If your cable has multiple wires, bind them together with some electrical tape just to remind you they go together.
Then, place the new battery in its place. If the posts are on the top, place the felt pads over the terminals and push them to seat on the top of the battery.
Unless your tie-down device was a shroud that enclosed the terminals as well as the battery, replace the tie-down device now.
Clean the battery cable connectors. Your battery terminals should be shiny new, but the clamps may not be. A wire brush and, if needed, some baking soda and water solution should get them good as new.
make a note of the date on which you changed the battery. The next time the battery fails, this will be a good indication of whether it’s an expected failure or whether it’s premature and the rest of the electrical system requires attention.
Place the clamps over the post (or start to thread the bolt in side-mount batteries), beginning with the positive terminal. Start with the positive terminal so that while you’re working on it, it can’t short out to the chassis by accident, since the chassis isn’t yet connected to the battery.
Then move to the negative terminal. Here, it doesn’t matter if your tools short the terminal to the chassis since shorting it to the chassis is the entire point of installing the negative cable anyway.
Give each terminal a covering of petroleum jelly, to help prevent corrosion.
If your tie-down device was a cover of everything, replace it now.
Make note of the battery replacement date
Finally, make a note of the date on which you changed the battery. The next time the battery fails, this will be a good indication of whether it’s an expected failure or whether it’s premature and the rest of the electrical system requires attention. Here’s more on how long vehicle batteries last.