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I changed the battery in my 2005 Volvo S80 back in August 2016. There was an old Genuine Volvo battery with a sticker date of 08/2006 that was removed. The battery posts and cable clamp were in pristine condition. I replaced it with a EverStart Maxx Lead Acid Automotive Battery, Group Size H8 and when I inspected the battery back in November 2017 I found a ton of corrosion on the post and terminal clamp.

What exactly is this material at a chemical level? I can see that the terminal clamp's metallic plating had dissolved off to reveal the underlying copper, and I'm guessing that Cu atoms got into the mix somehow to cause the light blue shade in the forming crystals seen in the images below.

Where did all this matter come from? Did my battery leak some kind of liquid that evaporated and left behind these salts, or was water taken out the atmosphere? What's going on here at a chemical reaction level?

battery terminal corrosion with unknown chemical salt looking stuff battery terminal corrosion closeup negative battery post after clamp was forcibly removed clamp after removed from post with corrosion still present clamp after corrosion thoroughly cleaned

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The battery is a lead / acid battery and the acid is sulphuric acid.

So, all the deposits you see are products of reaction - copper sulphate etc depending on the metals being corroded - you mentioned a coating that has been eaten...

Preventative maintenance would be to remove clean and then grease, with a petroleum based grease, all the surfaces and refit.

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    So is that to say the seal around the base of the negative post had sulphuric acid erupt out of it and begin to eat up my terminal clamp? – jxramos Feb 19 '18 at 15:37
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    basically yes, the seal is not perfect and vapour gets through... – Solar Mike Feb 19 '18 at 15:38
  • @jxramos - Seems to me the caps would exhaust a LOT more than around the post ... in fact, if you aren't seeing any type of liquid, I'd suspect almost all (if not all) of the gases are emitted this direction. It's the whole reason the caps are vented in the first place. For more information about what's going on, you can see this answer. – Pᴀᴜʟsᴛᴇʀ2 Feb 19 '18 at 21:59
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As you suggest , copper corrosion products will very likely be blue. Because the lead coating has been corroded , I expect most of the white corrosion products are lead sulfate in some form.

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