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Old 05-16-2021, 05:12 PM   #1
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Black gunk under my battery caps.

I was checking the water level in my FLA batteries and wondered what the black film on the underside of the caps is. The PO installed Water Miser caps and they appear to be working. No water necessary after a year. The PO left two gallons of distilled water next to the battery box, which now seems like a 30 year supply.

The caps are bright yellow and have a sticky layer of black stuff on them. I've never looked closely at the underside of battery caps (and never had bright yellow caps) so maybe I've just never noticed. It seems odd that battery acid and distilled water would have black sticky stuff percipitate out of solution. I would guess that to get on the underside of the caps it would be deposited from bubbles popping on the acid surface (charging).

I cleaned some of them, mainly because I was concerned that an accumulation of the gunk might clog the tiny breather holes on the caps. When cleaning, the sticky stuff wasn't water or alcohol soluble. Dawn dish washing soap sort of worked, but only by keeping the stuff that was smeared off from reattaching. It kind of reminded me of The Cat in the Hat.

Any chemistry types have an idea as to what this gunk is?
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Old 05-16-2021, 05:28 PM   #2
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My guess would be some kind of reaction (disintegration) of the rubber seals inside the "Miser" caps???
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Old 05-16-2021, 08:05 PM   #3
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pretty sure it's lead oxide
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Old 05-16-2021, 08:27 PM   #4
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Greetings,
Mr. MF. I think the black is lead oxide, as well but I don't know what makes up the "greasiness". I've seen the same "stuff" under my battery caps and just wiped it off.


Rather than speculate and in lieu of any TF chemists commenting you might either call your battery supplier or Water Miser.


https://doyleshamrock.com/contact-us/ Ask them what the gunk is and how to properly remove it.
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Old 05-16-2021, 08:39 PM   #5
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one of lead's properties is a certain lubricity...my thought as to why it's 'greasy' feeling.

My understanding this is just something that happens with some older batteries as they degrade.
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Old 05-16-2021, 09:02 PM   #6
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Greetings,
Mr. s. "Lubricity". Now there's a $2 word. Thanks. Perfect description.
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Old 05-17-2021, 05:21 AM   #7
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"My understanding this is just something that happens with some older batteries as they degrade."


The black coating on the caps is a sure good sign the batts are charging , its normal .
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Old 05-17-2021, 07:27 AM   #8
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Best guess because I have AGM batteries.

Soak, wipe clean and rinse. Make sure they are dry before reinstalling.

You could also discuss this with a battery shop too.

One the submarine, the lead acid batteries, I do believe there was a schedule for doing this and they used distilled water. The entire sub used distilled water for everything.
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Old 05-17-2021, 10:15 AM   #9
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The batteries are Dyno. They are in Seattle by Fisherman's Terminal and I'm in Seattle today. Maybe I'll stop in and ask them.

Wiping the stuff off didn't seem like a good idea. It just smeared the goop into the tiny holes that operate as the vent. Maybe Dyno will know the "fix." Hopefully, the fix isn't "don't touch it!"
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Old 05-17-2021, 04:20 PM   #10
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I stopped in at Dyno and was told that the material was "negative plate expander" and was not really a problem, just a normal sign of battery aging. If the batteries were overcharged, it could be "excessive," although the ultimate indication of overcharging would be early battery failure. So maintaining the water level, use a hygrometer, maybe stress test the battery, watch the charge cycle, monitor, etc. are all more important than the black goop.

I thought that lead oxide was alway red, as with the red lead oxide paint I used on wood boats. Turns out that there is a black lead oxide used in battery production as shown in the final entry of this Wikipedia post. One thing less to worry about.
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Old 05-17-2021, 06:51 PM   #11
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Quote:
Originally Posted by skyhawk View Post
pretty sure it's lead oxide
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