I need help-

I have the actual MKDS cartrdige, and a save for it, but to save space in my pockets, I'm getting roms for every game i own, which includes MKDS, However, I want to use m .sav file with the MKDS ROM on my M3. I converted it to .dat and renamed it to match the rom, but, here's the problems and methods I've tried-

*Patch rom with GM, blank MKDS .dat save file is automatically created, I overwrite the blank .dat with my original .sav that has been converted to .dat and renamed the same as the blank one.
RESULTS: The rom just boots, and doesn't recognize the save even being there. It only recognizes the blank one(wif I keep the blank oneand don't overwrite it).

*Put the .sav(now .dat) already renamed onto my MiniSD card, use the GM to patch the ROM and write it to my cart,.
RESULTS: but then it just overwrites my .dat(the .sav).

*Just put clean dump ROM on m3 with my .dat(.sav version).
RESULTS: Two blank screens after starting rom

So, it appears as though the ROM needs to be patched with the GM(der) but it seems as though after the rom is patched and a blank .dat is created through GM, the rom recognizes only that .dat file, like it has some other code in it from GM, so it won't work with my .dat I try to overwrite it with. So, does anyone know how I can use my .sav(now .dat) with my MKDS rom?