U cant use the .sav from the Gba Emu from the DS2, here is how u can play ur save on ur PC (it worked for me)
Saved using IN-GAME save (real save, not using NDSGBA real-time save). The output of that is .sav, so I dragged the .sav with the .gba on my computer, and I ran the game and loaded the .sav using REAL SAVED FILE (not the real-time save)