Car battery: Crud forming on + terminal

So, the positive terminal on my battery has been collecting a whitish, pasty substance. Everything will be fine and then out of the blue the car (Jeep Grand Cherokee actually) won’t start. I need to, about twice a year until recently, remove the positive clamp, clean it and the terminal with sandpaper, and then reconnect.

Recently though, this needs to be done every few weeks! I also have cleaned the negative terminal in the same manner a couple of times, but it’s definitely the positive terminal that is the resistive path.

What is the cause of this? Could it be that a poor ground connection somewhere perhaps?


This is a normal byproduct of the electro-chemical reactions going on in the battery and the car’s electrical system.

You can go to your local auto parts store and get a set of felt pads to place on the battery terminals which will inhibit the formation of said crud.

Is the crud on the + terminal greenish in color? Like … oxidized copper, perhaps?

It’s normal, but probably not every two weeks! The battery may be cracked or leaking electrolyte, or the alternator is overcharging? Might have your Cherokee’s electrical system checked out.

I’ve heard of perhaps smearing Vaseline (or an actual product intended to prevent corrosion) but not felt pads. Where do they go, over the clamp and terminal? Is Vaseline a good idea?

No, as stated, it’s whitish.

We have always used grease to coat the terminals and posts. It is water proof (unlike Vasoline) and keeps oxygen from the metal. Works very well.
The felt pads slid down over the posts and the clamp sits on top of it. You are probably aware of the old “pour Coke on them” to clean off the build-up. This works also.

So, what exactly is the felt doing? If it’s intended to insulate wouldn’t rubber, or about a dozen other thongs work better?

I figured anything to do with Coke cleaning this, or removing rust from that, was just urban legend. Any cites?

Other things, obviously.

At this site they state

As they say, it’s the soda. 7up or baking soda will also work to counter the acid.

I’ve always used baking soda.

The felt pads are treated with some kind of chemical to inhibit the reaction. There are two pads, usually a red one for the positive terminal and a green one for the negative terminal.

Please, please don’t do this. I’ve cleaned up after this 3-4 times.

“Your terminals look clean, so it’s probably not that.”

“Yeah, they’re fine, in fact I just cleaned them last week…my brother-in-law told me about using Coke…I almost didn’t believe it, but it worked great!”

It is only a cosmetic fix, and leaves a nearly invisible insulating layer of dried cola between the terminal and the clamp, but erases the clue of the corrosion buildup. It can also cement the clamps in place, making them very difficult to pull without damage.

Instead spend about $20 at the auto parts store for:

-A clamp puller. Failure to use one will likely result in cracking the case around the terminal when you try to pry the clamp off with a screwdriver. This may be what caused the trouble in the OP, in fact.

-A battery terminal cleaning wire brush. This has a (covered) male and a female end, and will get you down to shiny fresh lead with only a few twists.

-Terminal spreading pliers. Lead is not springy, so and these are the best way to open the clamps prior to reinstalling them. Trying to beat them down the tapered post is the other way to crack the seal around the terminal.
I keep this set of tools in each car. They have been used on other peoples cars about 5X as often as on mine.

The red and green felt washers, DO work well, in my experience. As does the aerosol spray terminal coating. (I like the butyl rubber based TRW product best, but don’t know if it is still available)

The felt pads are treated with a corrosion retardant chemical. They work for a while, but not permanently. They also restrict getting the cable ends fully down on the battery posts. I don’t like them.

Battery terminal protector is available in spray cans from auto supply stores. It also is not permanent, but it’s extremely easy to apply.

Vaseline and grease work, and are cheap. However, they are messy.

As mentioned above, very rapid build-up of corrosion usually indicates a faulty battery and/or overcharging. Testing the battery and charging system makes sense.

The most efficient and thorough way to clean the battery posts and (especially) cable ends is with a battery terminal brush. Coke, or spray terminal cleaner, can sometimes help, but DON’T LET THOSE CHEMICALS GET INTO THE BATTERY’S CELLS. I use a terminal brush, a steel wire “toothbrush,” and small picks and scrapers to get ALL the corrosion off of and (for non-solid cable ends) out of the cable ends. You want the mating metal of the post and cable end to be clean and SHINY.

If the posts and cable ends are clean and shiny, the cable ends are fully down on the posts (the posts should poke through at the top), and the cable ends are properly tight, I don’t see how the corrosion could affect it in just a few weeks. I suspect they haven’t been clean enough and/or tight enough. It’s a separate problem from rapid corrosion build-up, but it does affect the battery’s susceptibility to corrosion.

I vote for overcharging the battery - this causes the electrolyte to “boil” and outgass through the vents. Some corrosion is normal, but not in that time frame so this points to a problem with the charging system, or maybe a leaking battery as pointed out above. Another remote possibility is that you have moved from a relatively warm climate to a colder one or vice versa, as I understand it batteries are constructed differently for warm or colder areas.

I haven’t moved, but this problem has existed since I changed the battery a couple of years back. Sounds like a damaged, or cracked case could be responsible for leaking gasses that are possibly exacerbating the situation. I’ll try some Vaseline or other protective coating and report back…

Thanks all.