Hi looking to buy a gameshell, it can be built or unbuilt. Please let me know and I will respond promptly. Thanks!
Heishiro
Hi Heishiro! I have a Red one built that I bought end of 2020. It has Pokemon FireRed and Metroid Fusion on it, but sadly, the battery doesn’t work anymore and I haven’t been able to find a suitable replacement 
I’m not sure if you’re interested? I live in the US.
-Cornelius
There are plenty on Amazon, the type of battery is BL-5C
Hi Petrakis,
I’ve tried multiple times with them, but they still don’t seem to work.