Once your Game Boy Advance SP battery has gone bad, and you start to look for a replacement you will see it is impossible to find original batteries since they expire if you do not keep charged with a minimum level of charge.
Compatible batteries may be an alternative. However, some manufacturers may lie with the real capacity or their quality is not good enough.
If you have changed the screen for a IPS screen, or the charging port for a USB-C port. I am sure you will also want to replace the battery and make your GBA SP perfect. This kit helps you to install any li-ion battery, however the best option is the 603048 which has 900mAh, that is 300mAh more than the original!
https://shop.giltesa.com/product/game-boy-advance-sp-battery-adapter-kit
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Check the LICENSE.md for more information.