Blue on battery posts; what causes it?
 

What causes this blue build up on my battery posts? Oxidation? I've cleaned them in the past and lubed with dielectric grease but it returns.
http://forums.pelicanparts.com/uploa...1454994383.jpg

I believe that is copper sulfate. The copper in the cable reacts with the sulfuric acid in the battery.

The top of your battery looks nasty. You must have a leak or excess charging and bubbling of gasses and acid.

Do you clean the clamps also?

From Wikipedia
"Sometimes, it also happens that copper clamps or ringed copper terminals which are used to connect battery with wires corrode. Copper itself is not reactive even if dilute sulphuric acid is poured on it. But when electricity passes, it reacts with sulphuric acid and produce copper sulphate ( CuSO4 ) along with water and sulphur dioxide gas. The equation of this chemical reaction is following:

Cu (s) + 2 H2SO4 (ℓ) → CuSO4 (aq) + 2 H2O (ℓ) + SO2 (g)"

Mix Baking powder and water to clean that up then thin coat the ends with a grease (i use bearing grease)

Oh, pretty!

I'd also recommend getting some of the felt washers that PEP Boys sells and put them under the clamps. I think you usually soak them in ATF to help form a barrier to the fumes.
I'd pull the caps off and see if you have some low electrolyte levels in the cells.

Baking soda.

You do not need to soak the felt rings.
Put them on the posts, tight to the case.

They work well.

Check your battery and voltmeter; you may be overcharging.
Looks like a sealed battery.
How old is it?

good catch.

just don't let the baking soda get down into the cells.

I think I read somewhere that cola will clean that crud off as well but then you have to clean the cola....

Chia posts!

so your battery is making more little batteries? anyway, WD40 will also keep them clean, after you clean them up once every 10 years or so.

It's my Honda DD appliance. It's only rhe second battery since '02. I put it in Dec '09. Have not checked levels, but will do so now. I thought the dielectric grease would keep that copper sulphate at bay. I'll clean again and might try the felt below the clamps. I'll try the baking soda for cleaning this time. Battery is likely nearing end of life.
Thanks for the replies.

Henri - You'll probably find the clamps are toast under the blue stuff. Don't ask how I know. I'd say get a new battery since you're going to be cleaning the cable ends. It'll save you time since the battery is probably compromised already if it's from '09.
My '02 Accord went thru 2 batteries in 9 yrs of its 153k mile life while I had it.

I have found that the felt pads with NO grease works best.

Hot water will work as well. New conventional batteries come with a sealed top (you can still open them and add water) but have a vent tube that collects any gasses and it goes down below the battery to vent. Just replaced the battery for my 08 Chevy pickup and the new battery came with the vent tube.

+1
I have seen old timer mechanics place a penny between the connector, and post. I have also seen them use grease instead of dielectric. Should prolly clean them. The resistance is super high and will cause a no start.

why?

i think the alt is charging on the high side. put a V-meter on it and check it out.