this is the one i got and it’s worked well for my ags 101, got around 6 hours from the first time charging it with brightness on and volume up (tested it that way i usually play without brightness and only sometimes with volume but i haven’t tested the time on other conditions)

https://www.amazon.com/Rechargeable-Lithium-ion-Compatible-Game-Boy-Advance/dp/B00FJ2WOJE