Review on Rechargeable Lithium-Ion Battery Kit With Tool Pack For Nintendo GBA SP/Game Boy Advance SP - 850MAh Capacity by Joe Lantz

Leaving a review so people know this is a legitimate product (at least the one I got).

Didn't do any extensive testing or anything but this seemed to fix the issues I was having on my SP with a dead batteryUpdate:So far battery life isn’t bad! After an initial full charge, I played a little Pokémon TCG (GameBoy Color game) here and there and I was also able to just about get through the entirety of Metroid Fusion (3 hour play time) before the red light came on. I didn’t wanna run until I died because I was on the final boss and didn’t wanna lose my progress!Overall I think the battery life is pretty good!