First of all, thanks to everyone who is going to reply to this.
After finding out the ridiculous prices of GBA flashcarts, I eventually decided to give a chance to this tiny console. After checking the terrible original FW, I flashed Opendingux and installed GBC and GBA (ReGBA 04/30/19 version). Both v.2.7 and v.3.0 seemed to work, so I installed the latter. Apart from one very demanding game (FFVI Advance), all the roms I tried ran quite flawlessly, and I cannot complain about this 25 $ machine, which instead has suprised me with its vivid colours and its nice screen.
I have only two silly questions:
1. The wrong battery calibration is no big issue to me, as I have experienced the same thing on my rockbox'd mp3 player, so it's ok. Though, does the led turn from green to red when it is actually short on battery, or will it shut down with absolutely no warning at all?
2. I don't like savestates, preferring saving my progress directly from the game options. I noticed that in ReGBA I need to close the emulator after saving, then turn off the console from the Power Off toggle and only after that I can switch it off. Otherwise, my .sav files get corrupted. Is there a way to avoid that? Maybe an updated version of the emulator? Am I getting anything wrong? GBC games have no corrupted files problem at all, even when I brutally shut down the console.
Thank you in advance and let's keep supporting Opendingux!