>>55329031>and i dont wanna delete my save to get a replaced internal clock to actually workyou need a DS/DS Lite and a DS flashcart, but it's possible to fix the battery and get the clock to work again. there's other methods described in the comments too.
https://gbatemp.net/threads/how-to-reset-the-rtc-in-gba-pokemon-games-after-replacing-the-battery.558620/ 