NCR18650 Discolored. Leaking?

I am stripping cells from old batteries. I have a large quantity (about 300 pounds) of 4 cell packs with most containing Panasonic NCR18650 2900mah cells. A good portion of the cells have some brown flaky stuff on the positive terminal that almost looks like the cells vented. They all came out of the packs though with 3.4+ volts. I charged about 100 or so of them now to 4.2v then discharged to 2.8 and they still have 2700-2800mah capacity. The discoloring on the terminal has me slightly concerned though. Out of 100 cells, not one tested bad, none got hot, none had high resistance, etc. Is it possible these cells were just overcharged at one point or got too hot for some reason? I assume they're fine to use considering I tested 100 of them thoroughly and the outcome was good?

Link: http://industrial.panasonic.com/cdbs/www-data/pdf2/ACI4000/ACI4000CE17.pdf

I'm no expert so I'm going to stick around and see that other people say but that doesn't look good to me.

I'm going to stick around too. I'd like to see what people reply, just in case I see the same on one of my batteries. I'd be afraid to use the battery in the picture, that's for sure. I'm new to 18650 though.

I'm new too, hence why I'm seeking advise. They seem to be working great though. I re/discharged a few of them several times now just to see what would happen. No problems at all. The previous application for these packs was robotics. I think they were heavily abused and maybe overheated due to high discharge or overcharging.

Could be simply rust as I've had some batteries I salvaged from tool packs that got wet and 2 of them were rusted bad, one so much the bottom fell right off of it. If it is surface rust it may be fine but if it extends deep into the metal I would pitch the batteries myself as it can both let fluids in/out and also fall apart under stress.

Lynx_Arc said:

Could be simply rust as I've had some batteries I salvaged from tool packs that got wet and 2 of them were rusted bad, one so much the bottom fell right off of it. If it is surface rust it may be fine but if it extends deep into the metal I would pitch the batteries myself as it can both let fluids in/out and also fall apart under stress.

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These packs were used in robots that conducted sewer inspections, so it's very possible since they would have been exposed obvious moisture. Do you happen to have pictures of the rusted cells that we could compare?

lolmonkies said:

These packs were used in robots that conducted sewer inspections, so it's very possible since they would have been exposed obvious moisture. Do you happen to have pictures of the rusted cells that we could compare?

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I threw away the rusted cells they were bulging a little under the wrapper even on the sides. If they were used in sewer inspection then the damage could be greater than it seems as people use harsh chemicals to clean drains at times that can corrode metals easily. My advice is to choose one cell and fully discharge it and pull the wrapper off and inspect it fully.

lolmonkies said:

These packs were used in robots that conducted sewer inspections, so it's very possible since they would have been exposed obvious moisture. Do you happen to have pictures of the rusted cells that we could compare?

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Sewer inspections you say? This is not rust, this is CRAP!

Lynx_Arc said:

I threw away the rusted cells they were bulging a little under the wrapper even on the sides. If they were used in sewer inspection then the damage could be greater than it seems as people use harsh chemicals to clean drains at times that can corrode metals easily. My advice is to choose one cell and fully discharge it and pull the wrapper off and inspect it fully.

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The cells are pristine. The wrapper came off several as they were glued together and hard to get apart.

vadimax said:

Sewer inspections you say? This is not rust, this is CRAP!

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Funny...

I guess I'll just keep charging them and monitoring closely. Thanks guys.

I had some Samsung cells with such leaks. While they was at 60-70% of their capacity, their internal resistance was quite high, 500-600 milliohms, so they heated up badly when charging or discharging. I've discarded them.

I was going to suggest unwrapping and testing each battery before use (better safe than sorry) but when I re-read your first post and saw "300 pounds" (approx. 3000 batteries?), I guess suggesting that would be silly.

I would think the safest thing to do would be to simply recycle the rusted ones, since it would take way too long to check each one of them and I wouldn't want to use a battery that might vent or explode. Maybe I'm overly cautious. :shrug:

Update: Breakfast delayed me from posting what I wrote, so I missed the OP's last post. I hope everything works out well.