Pokemon games for the GBA (Game Boy Advance) have an internal RTC

chip with a coin battery to keep track of the time when the console is

powered off.

What happens when the internal battery runs dry? How to fix it?

Is this enough to completely restore calendar-based events?

Tools:

https://github.com/megaboyexe/GBA_RTCRead

https://gbatemp.net/threads/how-to-reset-the-rtc-in-gba-pokemon-games-after-replacing-the-battery.558620/

Swapping battery instructions https://www.youtube.com/watch?v=1piXd3ffwug

Additional resources:

https://www.youtube.com/watch?v=jzauCmOvF_U

(few mistakes about here)

https://www.youtube.com/watch?v=TrIAyAKg2S0

(followup videos with corrections)