I don’t know what happened…
Weird wrinkled plastic wrapper. No leakage or bulge. The other side:
Maybe this thing got short-circuited and became very hot? Maybe the wrapping has some heat-shrinking properties on purpose, to report this condition even if you look well after things have cooled down again?
I’ve been switching to Eneloop AA batteries everywhere since over a year now, due to the three nice chargers I’ve got. The advantage over NiCad and NiMh is that these really retain their charge for more than a year – perfect for wireless sensor nodes. When fully charged, each cell supplies 1.3V @ 1900 mAh. I’m also re-using these batteries over and over again in the wireless keyboards and mice we have (my mouse runs out once a month).
But that’s the end of the line for this one!
Looks like a short-out overheat. I did the same to two NiMH AAs when I accidentally threw my house keys and a handful of small change into the side pocket of my rucksack. I forgot the spare batteries for my camera flash were already in there.
Whoops.
You are correct in assuming that the wrap of the white Eneloop batteries is a heat shrink.
Be careful, because this only applies to the WHITE eneloop batteries!