That's kind of interesting about medical packs having this type of corrosion.I'm processing these medical packs from Battery Hookup - and I'm running into a number of cells like this:
where the corrosion is around the top ring but doesn't extend into the positive top area.
I'm with Korishan on this I would be very picky about using any cell that has any surface damage i.e rust, dents, etc.Personally I would recommend not using any cells that have rust on them
OK I'm going with this explanation - e.g. external humidity on 'defective metal casing' is causing this corrosion rather than damaged electrolyte spewing gas thru the vents.Corrosion, rust, can happen with just high humidity in the air. It doesn't have to come into contact with drops of water. I know this, because I live in Fl. We have high humidity on the regular. And I've had things rust being on the porch, w/o any rain for weeks. Just from the 80+% humidity on a daily basis.
And if the cells were in a cool area, and then moved outside, then condensation can occur which would actually suck the water under the wrapping.