I was a Genius for many years. If we broke something during a repair that couldn’t be fixed (like one of the side buttons) we would replace it, but usually for the price of whatever the initial repair was. So if it was a battery replacement, you would get the whole phone for battery cost. I’m in the U.S. though. Australia has some pretty serious consumer protection laws in place, so I wouldn’t doubt if they have to replace it at no charge by law.