It's not the prettiest look but I managed to get a 1600 mah rechargeable battery pack in my GBA 101 : r/Gameboy
Gameboy Advance GBA USB-C Rechargeable Battery Pack - Etsy
Game Boy Advance DIY £14 Rechargeable USB Battery MOD : r/Gameboy
Game Boy Advance Rechargeable Battery Mod : 6 Steps - Instructables
CleanJuice Game Boy Advance Rechargeable Battery Pack | RetroSix
New Rechargeable Battery for Nintendo Game Boy Advance SP - Etsy
CleanJuice Game Boy Advance Rechargeable Battery Pack | RetroSix
Rechargeable Battery Pack With Tool Kit For Gba Sp Lithium Battery For Nintendo Gameboy Game Boy Advance Sp Console - Buy Battery Pack For Gba Sp, For Gameboy Battery,Battery For Gameboy Advance Sp
Amazon.com: Gameboy Advance Rechargeable Battery 1500mAh USB-C Lithium LiPo Mod for Nintendo GBA / AGB-001 (Black) : Video Games
Amazon.com: Gameboy Advance Rechargeable Battery 1500mAh USB-C Lithium LiPo Mod for Nintendo GBA / AGB-001 (None (Battery Only)) : Video Games
Amazon.com: Gameboy Advance Rechargeable Battery 1500mAh USB-C Lithium LiPo Mod for Nintendo GBA / AGB-001 (None (Battery Only)) : Video Games
Gomadic High Capacity Rechargeable External Battery Pack suitable for the Nintendo Gameboy Advanced SP / GBA SP