Oh actually it is really easy, just rename the desmume save file which has the extension .dsv to .sav, copy it to where ideas will search for the battery save files (aka the .sav files), if you run the emulator for the first time you can set where do you want the emulator to store the .sav files. Now with that done just open the rom but before click on the play button on the toolbar go to the options menu and in save type set it to eeprom 512kbits and then click on play button to run the rom.
It is important to not disable the sound till you loaded your game, I had the issue that if I disabled the sound before that, even though the game loaded well I couldn't go to any other screen and my character walked through the other characters and couldn't talk to them.
Now to get a decent speed, go to options menu and set the frame skip to 3, that will give you a decent speed