Back up or Flash?

I'm going to buy some old GBA games and I dont know if they are using back up or flash memory for saving so I'm afraid about their ability to save. The games I'm going to buy are Metroid: Fusion (J), Metroid: Zero Mission and PKMN: Emerald but I know that Emerald uses flash. Does anybody knows what kind of saving Metroid games use?

if its battery its not difficult to change the battery if necessary.