Testing the Rayovac GBA SP battery (And a few others!)
Channel: makho
Date: 07/05/2020

TL;DW: the battery is pretty good. It's a lot pricier than my DIY option though. 

Edit 2021-04-20: So I have edited this whole description because Batteries+ has since discontinued the Rayovac battery and because new alternatives have appeared that are pretty good. I have not tested the new battery that has replaced the Rayovac battery so I cannot comment on if that battery is specced truthfully or not. 

These are decent drop in alternatives: https://retrogamerepairshop.com/collections/gba-sp-power/products/gba-sp-game-boy-advance-sp-real-750mah-replacement-battery?variant=32435336544330

Originally the above link went to the generic green cells but capacity varies too greatly for me to recommend them. RGRS now carries newer cells with a black label and the capacity is much more consistent (albeit consistently less than what the label claims -- label claims 850mAh but they all tested between 750 and 800mAh actual). I recommend them if you need cheap, reliable drop in batteries. There are higher capacity options though, if you don't mind spending a bit more OR putting in a little DIY: https://www.youtube.com/watch?v=VjnONhSVvpA

The original link for Batteries+ no longer goes to the Rayovac cell and instead goes to a different one because Batteries+ has apparently replaced it. I have not tested the new battery -- https://www.batteriesplus.com/productdetails/mse10001

And finally, here is the reddit thread I made with my detailed power consumption notes. I'll be adding the values recorded here eventually but for now they should still be useful for extrapolation of other models or mods. https://www.reddit.com/r/Gameboy/comments/ehru1w/relative_power_usage_of_backlight_mods/