Best method to replace battery when device hasn't been used in years

Background: I recently went to our parents house since I was living at a different place now. While rummaging through my old drawers I found my old Nintendo Gameboy Advanced SP. When I saw it I wanted to try and repair it but my current problem is the battery.

I haven't used this device in years, probably even more than a decade. I've tried searching online what to do with batteries that are bloated but couldn't find any information when they haven't been used in a long time.

For the meantime, I've stored the device in a metal container with sand and placed it in a concrete room (as some threads have said).

What would be my next steps and how long do I need to discharge it before removing the batteries. I'm scared to open it since I've read what could possibly happen if I accidentally puncture the battery or when some kind of reaction happens.

Sorry I'm not really knowledgeable in these kinds of things, I would appreciate your comments and suggestions.

Thank you!