after googling quite abit about FFL1's rom data. it seems that FFL1 along with some odd roms that have NO SAVE-RAM according to their ROM data. their savegames work fine on real hardware, but emulators can't detect them at all. i'm guessing nintendo used some sort of obscure hardware RAM on those carts which modern programmers might not have any blueprints on. ===
update: oh nevermind, it seems that BGB emulator can save properly. but there's no way for me to use VBA's savegame or battery file because it's not actually saving the in-game savegame to a file for save it or export a battery file. it just creates an "empty" 1KB file that seems have no game data in it at all. weird. guess i'll try an updated version of VBA instead.