Sorry, I didn’t think to take a picture.
I took the 26650s out of L2 for charging and noticed what appears to be a pin hole in the base of one (-) and a thick brown liquid. I retired the cell and it’s outside, the other one looks OK but of course it’s no longer part of a matching pair. Is the electrolyte in these cells corrosive? I’m otherwise at a loss as to how it got a pinhole.
FWIW, it is a Basen 4500 mAH 60a max pluse (not a typo) current. I see no other identification.
That is messed up, a pic would be nice though.
I agree about it being messed up. I nearly pooped myself when I saw it. I don’t think they’re supposed to do that.
I can try. But I wiped it up.
The pinhole is almost in the center of the picture. There is a central brownish area, the pinhole that was leaking is at about 1:00 in the brownish orange, there is another small area at 7:00-8:00 as far as I know that wasn’t leaking. Despite me wiping up the ooze the outline of it can be seen.
https://i.postimg.cc/pTydZ2J7/26650-cell-pinhole-and-leakage.jpg
Sorry, the magic of posting a picture and having it show in my post continues to elude me. But click on the link.
(edited for clarity)
Weird, defective (exterior) can maybe?
When’s the last time you opened the light up before this? And about how many times have you charged the cells?
Was this cell at the tail end or closer to the head of the light? This may be stupid, but is it possible the brown liquid was rusty water? Where the water came from is another question…
Can you check the voltage of the cell? If it’s wildly different than the other one that would support the idea that something bad happened with the cell.
No water is possible from outside the light. but it wasn’t water, it was thicker, almost the consistency of motor oil but it wasn’t oil. The first thing I thought of was electrolyte but I have no idea what’s inside these cells other than something I never want to have go nuclear on me. I pretty much charge the cells not later than every month and the cells are near 3.8v when I stick to that schedule. But with the possibility of a power outage, as we have tonight and have frequently anymore, I charge more frequently; everything was OK last charge not long ago. There are 2 cells in the light and it was the rear of the cell nearest the LED.
The reason I charged the cells today was it was time, and we could get a power outage (wind storm), so I charged them. It’s just prudent. Today I’m charging everything and saw the issue with the cell.
I keep records on all of my cells and both of them have been in use since 2016.
Thanks for posting the picture BlueSwordM.
The one thing it could be would be grease, or silicon gel.
Maybe. But I have no idea how it would have gotten there. It sure didn’t act like grease or oil, but something thick and that could dry. Hence the outer ring that I couldn’t wipe off. But anyway, it’s outdoors in the rain right now. We’ll know more tomorrow if it was water soluble or not.
Can you actually find a hole with a toothpick or pin/needle?
If I remember I might be able to find something small enough tomorrow. But if it’s corrosion I doubt that it’ll be round and agreeable. You have no idea how much I hate poking a Li-Ion cell. I’m just glad it didn’t ignite in use.
It’s hard to see the center spot clearly…whether it’s a hole-hole or just some pitting/gouge. Is the end of the spring cut and positioned so that a sharp edge could be scoring the bottom of the cell every time you screw and unscrew the tail cap? I find lots and lots of springs like this and usually bend that cut tip slightly downwards, sometimes smooth it lightly with a grinding stone in a dremel if necessary. Is the spring clean…none of that good on any of the coils down lower? Looking at that orange ring on the can makes me think the stuff spread to the spring.
I can’t see a pinhole, looks like rust.
Rub it with some scotchbrite.
I would not be bothered by that in the slightest.
Li ion electrolyte smells like juicyfruit gum.
Lots of reports of li primaries and cr-xxxx cells outgassing enough to smell.
But i dont recall ever smelling this from a li ion unless i tore a hole in it pulling off deeply spotwelded strip.
Too late now. I didn’t put my nose anywhere near that incendiary “bomb”. It’s good to know in the future. I hope I never need that info’ again! 
But it’s in the grey matter.