Nikon camera battery pack expanded.what does this mean?

I have a Nikon camera battery pack (EN-EL8) that for some weird reason expanded. It's fairly new and what not, but I'm not sure why it literally expanded… (almost like a bloating of the battery pack). I've stopped use of it, but I'm just wondering what could have caused this. I've kept it in pretty good shape, away from sunlight and heat.

That's a first for me and I'm pretty active on all sorts of photography forums for the last 5 years. If it is indeed an original nikon pack I'd contact them about it.

If the battery is swelled up that's a pretty good indicator that it's gone bad - reason? Who knows.
Could be exposure to heat, could be another reason. But if it's swelled first it won't fit and needs to be replaced.

I agree if it's a Nikon original and if it's still under the camera's warranty (if the warranty covers the battery) get in touch with them.