1st gen ipod nano battery expansion

I recently found an old iPod Nano (1st Generation) that was sitting in a drawer, collecting dust since around 2006 or 2007. When it was in use, it was slightly damaged with a small dent on one side of the back. I also noticed the back was slightly coming off on the opposite side of the dent, but I assumed it was just because of the dent. Upon charging it, the opening got somewhat worse, so I unplugged it (remember 30-pin?), used my fingernail to pull it off, and was shocked to see that the battery had expanded to the point that I actually cannot put the back plate on again. Not only have I never really opened a piece of Apple technology this small, but I am also not really willing to remove the battery due to risk of fire or explosion. I have no replacement batteries, but this iPod is nostalgic to me and I would like to avoid throwing it away until it is absolutely necessary. Does anybody know how to safely remove the battery with the lowest risk of damage to the iPod? (I no longer plan to use it, but I would like to keep it in a safe space with the battery fully removed and disposed of.) Thank you in advance.