When you are in a battle that you are about to lose back to the home screen on your android device and kill the game via task manager then tap Final Fantasy III again and tap continue on the main menu. You should be at the same place as you were when you got in the battle with all the items and health you had before the battle.
Damage Display and Actual Damage Don't Match Past Max
Typically the max amount of damage displayed is 9999, but in reality the actual damage can go past this. You can see this if you get a scholar or a magic that can see your opponent's stats.
By using their ability and using an attack that flashes up 9999 damage display, you can see that the attack almost certainly takes more than that off their health.