Automotive Electrical:

Removing And Installing A Car Battery
To Replace Or Clean It

Disconnecting A Battery: There Is A Right Way...
Battery Maintenance Extends Life...


In This Article:

Related Articles:

Skill Level: 1-2 (Basic) Time Taken: About 30 Minutes

By Bruce W. Maki, Editor


When removing a car battery, the first step is to disconnect the battery cables. The negative cable should always be disconnected first, and re-connected last.

Remove The Negative Cable First,
Re-connect The Negative Cable Last:

Why? Because the wrench or socket is touching the live part of the electrical connector. There is a good chance that the wrench or socket handle will accidentally touch something. The entire car is connected to the negative terminal.

If your wrench is on the positive terminal and it accidentally touches anything metal, you will short circuit the battery. The voltage isn't harmful, but the sudden unexpected sparks will startle the $hit out of you, and could even burn you. There is so much current (amperage) available that your wrench literally becomes an arc welder.

If you disconnect the negative cable first, and reconnect it last, then the car is not electrically connected to the negative battery terminal. After that you can disconnect the positive battery terminal with minimal risk, because if your wrench touches any metal parts of the car there is no complete circuit, and nothing happens. The only risk comes from touching the other (i.e. negative) battery terminal.

While connecting or disconnecting the negative cable, you don't need to worry about the wrench touching metal parts of the car, because everything is at the same electrical potential. You only need to keep the wrench from touching the positive battery terminal. That's easy.



Disconnecting A Battery With
Side Terminals:

Side-terminal batteries, common on General Motors products, require a small socket or wrench to remove the battery cables.

This used a 5/16" socket.


Next: disconnecting the positive battery cable.

If that wrench touches something metal, there will be no short circuit.


Wire Colors:

The positive battery cable may be red, and the negative cable is normally black.

Don't judge by the cables... look at the markings on the battery. I have seen many cars with black cables connected to the positive terminal. I'm guessing that the automaker used black-insulated wire because it's a bit cheaper than red.

Even more confusing, I've seen a red cable connecting the negative battery terminal. I think this happened because somebody replaced a negative battery cable and used red-coated wire... perhaps because they didn't have any black cable handy. No automaker in their right mind would deliberately use a red wire for the ground wiring.

The industry standard with automotive wiring is Black = Ground (which is negative), and Red = Hot (which is positive).

This can be confusing when compared with wire used in buildings, where black (and other colors) are hot, and white is neutral, which has the same potential as ground.



Disconnecting A Battery With
Top Terminals:

This battery was installed less than two years ago, yet it's already covered in dirt.

Dirt on the surface of a car battery can create a pathway for a tiny amount of electricity to flow between the terminals. Eventually this minor current flow can cause the battery to become drained down.


To prevent the radio from losing its preset stations, I decided to try using this 12 volt portable power supply to keep power supplied to the car while the battery is removed.

I connected the black alligator clip to the engine, and the red clip to the positive battery cable.


I loosened the negative battery clamp with a 1/2" wrench.

I think most domestic cars require a 1/2" wrench for the battery terminal clamps.


Often the battery cable won't come off. DON'T twist the clamp, you might damage the battery terminal.

Normally I use a pair of prybars to pry open the soft lead battery cable end...


... Like this


A Better Way:

This is a battery terminal puller. It cost a couple of bucks.


The arms (arrow) go underneath the cable end clamp, and the center pushes against the terminal post on the battery.

Turn the handle and the cable end clamp lifts right up.


Then the battery cable can be pulled away.

Be careful... since the cable is so thick it often tries to spring back to its former position. I've had a battery cable spring back and touch the battery terminal. I make an effort to tuck the cable away.


Terminal Maintenance:

It's a good idea to clean the battery cable ends and terminals with a wire brush. The terminals and cable ends are made from lead, which corrodes readily. Corrosion can increase the resistance of the electrical connection, which can prevent the battery from charging properly. Corroded battery connectors can create so much voltage drop that the car's starter motor cranks slowly or not at all.

This is a battery terminal brush, another tool that costs only a couple of dollars.


Under the cap there is (or was) a round brush to clean the inside surface of the cable end clamp.

Even though this is mangled, it still works okay.


The bottom has this nasty-looking circular wire brush.


I pushed the tool over the battery terminal while turning it.

This took about half a minute.


Car battery terminal with minor corrosion.

Battery Terminals Get Corroded:

<-- Left - Before cleaning with battery brush.


Right -->
After cleaning with the battery brush.

Car battery terminal after cleaning with battery brush.


Removing The Battery:

Once the cables had been disconnected, I could take the battery out of the truck.

But first I had to remove the battery hold-down backet. There were two very long bolts (red arrow) that secured the bracket to the body of the truck.

This Dodge Dakota required an 11mm socket to remove the hold-down bolts.


Then I could remove the clamping bracket.


I just lifted out the battery with the built-in strap. Otherwise this is a two-handed job.

Car batteries are heavy! This thing must weigh about 40 pounds.


No Battery Hold-Down Clamp?


My first car had no battery hold-down clamp or strap, and since I drove like a freakin' yahoo the battery slid off its tray and rested against the alternator. The alternator pully carved a nice little groove in the side of the battery case, allowing half the battery acid to leak out of one cell. I came out of work and the car would't start... because one of the six lead-acid cells was half-dead.

A bungee cord or tie-down strap should work if the original clamp is missing.

(At the end of this article you can read how I fixed the damaged battery.)


Cleaning The Battery:

I sprayed some diluted Simple Green on the battery and used a small nylon brush to scrub the dirt and oily residue.

Any household cleaner should work here.


I rinsed off the battery with a garden hose.



While car batteries are known as "sealed batteries", they do have vent holes on the top. Avoid getting cleaning solutions under the cap around the vent area. Also avoid spraying water directly at the vents... I used the "shower" setting on my garden hose. I would avoid using the "jet" type of spray. Power washing a car battery sounds like a bad idea... there is too much chance of getting water inside the vents, and even trace amounts of minerals in tap water can contaminate the battery acid solution.

I may have gotten water, cleaning solution or dirt into the vents... so follow these steps at your own risk. But I've been doing this for years and my car batteries usually last 5 or 6 years before they need to be replaced.



I used a Sharpie Metallic marker to highlight the raised letters on the battery. This will make it easier to read when I'm jump-starting someone's car on a cold dark winter night.


Installing And Re-Connecting The Battery:

I wondered if silicone dielectric terminal grease was meant for battery terminals, so I read the package that I had in my supply of automotive chemicals.

Indeed, it is.


I applied some dielectric grease to the battery terminals and spread it around with my finger.

I also applied a thin film of dielectric grease to the inside surface of the battery cable ends.


I connected the positive battery cable first, and tightened the clamping nut with a 1/2" wrench. Don't tighten too much... the soft lead cable end can be damaged.

Lastly, I re-connected the negative cable.

The good news: By connecting the portable power supply to the positve cable (and grounding the black clamp to the engine) I did not need to re-program the stations on my car radio.


A clean battery with clean connections will provide the greatest possible cranking power on cold winter mornings.

I think it's a good idea to do this battery maintenace once a year, preferably before cold weather sets in.


Additional Battery Information:

Fixing A Cracked Or Leaking Battery Case:

Many years ago, when I was 19 and knew nothing about fixing cars, I reasoned that a recent invention called silicone caulking might work to patch a small hole or crack in the plastic case of a car battery. The package of silicone said that it released acetic acid while it cured... so I figured that if silicone released acid it must be able to tolerate acid.

I cleaned up the hole, applied some silicone caulk and let it dry for an hour. Then I went to my local garage and paid a whole dollar for them to top-up the acid in the leaking cell. That battery lasted another five years until I drove the car to the junkyard.


More Info:

Tools Used:

  • Sockets: 5/16", 11mm
  • Wrench: 1/2"
  • Prybars
  • Portable 12 Volt Power Supply
  • Battery Terminal Puller
  • Battery Terminal Brush
  • Nylon Brush
  • Garden Hose

Materials Used:

  • Dielectric Terminal Grease
  • Household Cleaning Solution (e.g. Simple Green, 409, Windex Multi-Surface Cleaner, etc.)
  • Sharpie Metallic Marker

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Written July 24, 2007