Rescue a Red save

[Fragor Caelestis]

A friend gave me this save file asking me why he can't put it back to his original cartridge after the battery replacement, the game simply won't load. I've tried PKHEX to see his pokémons but it gives me error, then I've tried opening it with HxD and I see that it's different from my savefile but I'm ignorant and I don't know if I can fix it or where to put my hand on, I don't wanna mess it up, I relatively new with that language I just know 2 or 3 things like the codes for the gameshark. There are a lot of FF and a bunch of yyyy here and there. Is it fixable or he lost everything just for a battery replacement? Can I rescue at least his pokémons? Can someone show me how to do it or can you do it? I know he has a venusaur at lvl 100 and a bunch of other pokémons.

Pokemon - Versione Rossa (Italy) (SGB Enhanced).sav