Instructions
Use the website listed in the Resources section of this article to look up the ROM of the game you are playing.
Click the tab that reads "ROM Information" and look at "Save Type." This will tell you the type of memory that is used in the game cartridge.
From the No$gba menu bar, select Options > Emulation Setup.
Find the option in the No$gba Setup menu that reads "GBA Cartridge Backup Media." If you're playing a Nintendo DS game, use the option that reads "NDS Cartridge Backup Media."
Use the pull down menu to change the save type to the proper setting.
Play the game normally and save using the in-game save function. A .sav file will be created in BATTERY folder of the No$gba directory if the game is able to successfully create a save.