A file with .sav extension is a Nintendo DS saved game file that can be loaded in Nintendo DS Game Emulators such as DeSmuME and NO$GBA. These files save the current state of the game which can then be loaded in the Nintendo emulators. Information stored in SAV files includes the game character name, experience points, levels completed, and in-game resources. SAV files can be loaded in emulators but the difference in versions of the SAV file can lead to generation of errors at the emulators. SAV files can be opened with DeSmuME and NO$GBA emulators.
SAV File Format - More Information
The Nintendo DS SAVE files are saved to disc in binary file format. Though these are not human readable, a HexaDecimal editor such as HxD can be used to open these for analysis. In scenarios where the SAV file can not be loaded into an upgraded version of an emulator, it can be opened in the Hex editor for removal of any unwanted padded data.