Each battery type was tested using 5 different batteries. They were charged completely then discharged by using an unmodded GBA SP with Zelda: LttP looping on the title screen. The life results were consistent across the board.

Green "850 mAh" batteries = These are the same batteries sold by most other sellers and they're not really 850 mAh. Mathematically they're closer to 180 mAh, hence the 3.5 hour life. If you don't believe me, there's plenty of youtube videos showing the same result no matter where you buy them or what packaging they come in. IMO save your money and don't buy these even from me, let alone more expensive from other sellers.

OEM Nintendo batteries = Genuine Nintendo batteries pulled from GBA SPs I scrapped or modded for other projects. These are original Nintendo branded batteries and will last you 11.5 hours on average.

White 900 mAh batteries = These are the batteries I use when I install IPS screen mods. They're truly powerful batteries that live up to their 900 mAh rating. For unmodded GBA SPs these will last you 19 hours.

If you have any questions, please ask.

Thanks for looking!