I can't confirm if this is how it is supposed to work in the original games, since i don't have access to one with a saved game atm,
But from what i read all over the internet, the move should fail when the user has less than 50% HP and it does fail, but I think the move should fail before losing the HP (i.e not fainting the Pokemon when the move fails).
But from what i read all over the internet, the move should fail when the user has less than 50% HP and it does fail, but I think the move should fail before losing the HP (i.e not fainting the Pokemon when the move fails).