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I had one like that. I don't use it anymore. Batteries are on the lower side of expenses in vaping. If you can get your hands on an external charger, you might be better off, too. Everything I've read about safety says to charge externally, so I do.
In my opinion that almost looks like e-Liquid contamination under the wrap. I can't tell from the picture but the insulator at the top looks kind of dark. If it is e-Liquid then it is a candidate for a re-wrap but as Huck said when in doubt throw it out! (Recycle)
That is a Sony isn't it?
For some reason, which no one seems to have worked out yet, this is a common problem with Sony's. The battery is fine to use, if you remove the wrapper those marks wipe off with a finger.
You can rewrap if you want, it is just an odd thing that happens sometimes with Sony's.