A save state is different from a save file, but it may turn out that this file is in fact a standard VBA save state, which would mean you could load it up in a regular instance of VBA and then make a save file that you can put onto the cart.  If not, try poking around in the file, there may be a VBA save state (or a normal Game Boy save file) hiding in there, possibly compressed (although VBA compresses its save states anyway) or with an extra header.

sooooo here's the thing. I've been writing some new lsdj stuff in an emulator (openemu) because it's fast and looks great on a big screen. Today I go to load up the .sav onto a cart and literally can't find it anywhere.

10 minutes of digging turns out that openemu uses a system-wide proprietary save state system, which is incredibly frustrating as the actual gb/gba emulator core it's running is VBA, which absolutely has a battery save function....

To anyone out there that might know better than I, am I doomed to chalk this one upto experience or is there a method of extracting the save somehow from openemu?

a few things i've tried in vain:

1. loading up the rom in it's current directory, in an actual copy of VBA
2. pulling one of open emu's proprietary save state's out, renaming it to LSDJ.sav and loading it onto the cart (bc y'never know)
3. tearing my hair out