What is the green corrosion on battery terminals?

Any chemists know the technical term(s) for the green corrosion that can form on an automotive battery terminal? I replaced a battery today and found a lot of very hard green corrosion that required me to scrape it off. A wire brush wouldn't budge it - I had to scrape it with a screwdriver tip and it took quite a while to knock it all off. I've never seen it so hard, almost like a hardended film.

Lead oxide?

Copper oxide.

Take some regular Coke Cola and pour it on the green area and watch it fizzle .... then try brushing it off with an old toothbrush

To avoid build up in the first place, use dielectric grease on terminals, keep battery top clean and dry(dust and moisture conduct between terminals) and tight fitting clean connections. some vehicles seem to be worse than others at corrosin buildup. namely Toyotas and Hondas with the metal band type top terminals.

What I have found as the most effective corrosion inhibitor on lead acid batteries is a good coating of silver Never-seize - it seems to totally prevent the green crud, and any other kind of corrosion from forming around the terminals or their connecting parts... I've had bolt-on terminals that showed ZERO corrosion on the bolts after several years of use. I've tried other sorts of regular and dielectric greases, those little red and green felt washers, and a few other ideas, none of which did as well. They also make a copper version of the same stuff, which isn't bad, but doesn't do quite as well.

Note that that oxide layer can cause some serious battery / electrical system problems - it is a fair conductor when cold, but not when hot, and it heats up with current - I've seen batteries that people thought were dead, that worked fine after having the terminals cleaned. I've also seen some that looked like starter or solenoid failure - lights would work OK, or nearly so, but the starter would just do the click and stutter routine - the oxidation would carry enough current to run lights, but would break down under the draw from the starter....

Now, any kind of car or motorcycle battery I install gets a layer of Never-Seize when installed. If I encounter any sort of dead battery symptoms, my first step is to pull the terminals, clean and Never-seize them - works quite often, if it doesn't the battery really IS toast...

Gooserider

The best way to clean battery terminals, when corroded, is to use a baking powder and water mixture. Rinse off and spay with battery terminal coating that most car parts stores sell. The above suggestions probably coat the terminals just as well. Once you get corrosion, it likes to keep coming back. I believe the corrosion is an acid and baking soda is a base.

I wanted to know the chemical makeup as I stabbed myself pretty good while holding the battery lead and scraping away at the hard green corrosion. My screwdriver slipped and plunged an inch or so down into my hand between the thumb and forefinger. I'm sure some residue from the tip was inserted into my hand. I washed it off and bandaged it up but a little worried about the chemical. I'm less worried about an infection (I seem to have a great immune system, 40+ years of stupid cuts and no infections) and just worried of some toxicity.

I would try drinking some water and baking soda to combat this situation..... just kidding, I hope your OK.

In the absence of an infection, you might just end up with more of a scar than normal, if any foreign metallic substance was carried beneath your skin. Your body will just wall it off, and there it will sit. I've got a black streak visible beneath the skin of my hand, where I accidentally injected myself with some grit from under the car. Hasn't changed in 20 years.

Most likely copper sulfate which is a hard green/blue crystal. Forms from hydrogen sulfide gas leaking out of the battery + copper in the wire...

http://en.wikipedia.org/wiki/Copper_sulfate

Copper oxides tend to be red to black depending on the oxidation state:

http://en.wikipedia.org/wiki/Copper_oxide

A small bit of sulfate is not too toxic - it was once used to induce vomiting. You will probably live ...this time. Though just take care the wound doesn't get infected.

Also, IMHO corroded battery terminals are a sign of deeper problems with the battery. A bat in good health generally won't put out enough H2S to cause any problems.

I stand (sit actually) corrected.

I agree, probably a copper oxide of some sort, but also likely has some lead in with it as well. Probably won't kill you, but might be worth seeking medical attention, as none of the stuff in and around a battery is going to be good for you...

Gooserider

You are fine re: toxic metals, both Pb and Cu. Check that you are up to date on tetanus though.

My 2000 Tacoma is now 10 years old and the battery terminals look just they did when I bought it 10 years ago.
Maybe it's the height off the ground, or I got a bad one.

I've tried those green and red corrosion inhibiter thingies years ago and they did seem to help. K-car and a Ford Escort.

Baking soda works to clean, just don't let it get into the battery.