i use my macbook at home, always on ac power with battery fitted in. its always fully charge. well suddenly my battery icon started to display ' calculating ' and soon after it showed the time left to a full charge. thing is i never unplugged, neither was there a power outage. so now my battery is showing is 90+% with 0:31 to go to a full charge, and my magsafe is displaying a orange light. is my battery dying or is there something i do not know ?