This is on my 1990 760. I posted it here because you 240 guys seem to be more active. I do have a 245 that is my daily driver if that helps any.

I can not figure out what is going on here. I clean this well, and in a couple of weeks it looks like this. The car always starts fine.

Anyone have an idea why?

Besides it being a bad battery I would check the charging voltage.

A battery can have a bad cell causing the alternator to raise the voltage.

Regulator could be wacky too!

Something really bad is going on for that to corrode that fast. Acid is jumping out of there for a reason.

Phil

Try petroleum jelly (Vaseline) on the posts to prevent corrosion.
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1980 245 Canadian B21A with SU carb but electronic ignition and M46 trans in Brampton, Ont.

Agree with Dan. Jiggle that post and I think you'll find it's a little loose wet at the base. Not so long ago I replaced the battery in the 850 for that reason. Seems a shame to waste an otherwise good battery, but that corrosion is not good for cables.

Maybe you have some warranty left in that one?

-Will
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854 - 244 - Mini

Probably a loose post and acid is leaking, time for a new battery.
Dan

It was a cheapo from Sams Club. I bet you are right!

When you do change out the battery, brush off all that crud and soak the whole connector and adjacent cable in a baking soda solution bath, and rinse well.
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In God We Trust. Everyone else, keep your hands where I can see them.

I second that, very good advice. In addition, I smear the terminals and the connectors with a thin layer of conductive copper paste.

Erling.
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I do the baking Soda cleaning, but not familiar with the conductive copper paste. This sounds like a good idea, what is a brand name and does anyone know the availability in the US?
Thanks
Dan

As mentioned earlier, Vaseline is much cheaper and it works. Been using it on my Volvos, Mercedes and Toyotas for 30 years.

Once upon a time there was an industrial grade of Vaseline with a coarser texture and a higher melting point than the stuff you smear on babies' chafed bums, but I haven't seen that in years. When I used the standard Vaseline on my cars it melted and ran pretty quickly, making wheel bearing grease a better alternative for me. These days I just buy the spray-on Permatex goop.
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In God We Trust. Everyone else, keep your hands where I can see them.

Sounds good but I don't think vaseline is conductive?
Thanks
Dan

I was just comparing cost and availability against desired outcome:

Desired outcome - reduced corrosion at battery terminals

Vaseline cost & availability - about $1-2 for a small jar anywhere

Copper paste cost and availability - probably more than vaseline and probably found at fewer locations.

Not sure I understand the value of a conductive paste at the battery terminals.

That's my 2 cents worth. Cheers!

I agree with you JR. But many, especially on 7/9 forum, will not.

I believe a clean lead to lead terminal-to-battery-post joint doesn't need anything in between to promote conductivity. The typical "conductive grease" such as OxGard (zinc ointment) is sold to electricians making dissimilar metal connections with aluminum wire. The grease fills the interstices in stranded cable and inside clamping terminals to exclude moisture and thus slow oxidation and galvanic corrosion. If you stick your ohmmeter probes in a dollop of OxGard or copper anti-seize, you won't get a reading. Know that GB does not need to make any claims for this property as they have a fan club inventing reasons to use OxGard on automotive wiring and other non-aluminum applications.

The vaseline or grease (dielectric grease, Sil-glyde, moly, OxGard, anti-seize, whatever) serves to protect the terminal from corrosion by excluding moisture.
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Art Benstein near Baltimore

When fish are in schools they sometimes take debate.

I have never used a compound on battery terminals, just a clean roughed up surface on both parts has always worked for me. I was intrigued by the apparent snake oil characteristics of better conductivity. but I do like the anti corrosion part. Have to give it a try.
Dan

The loose post in the OP's case provides the extreme case for terminal corrosion. Normally the atmosphere around the terminals is bad enough from the battery vents, but I've seen a terminal grow fuzz like this in a couple weeks when the post is loose. At least I've learned to throw away gloves and rags after cleaning up a battery with them. What an easy way to destroy a pair of jeans.
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Art Benstein near Baltimore

To write with a broken pencil is pointless.

I never knew the stuff existed but the value is a better connection between the battery post and the connectors. Toss in corrosion protection and it seems like a win win to me.
Dan