I have a late 2013 2.3ghz retina 15 purchased about 2~3 weeks ago. I use Coconut Battery to track the battery performance. Since I've had it, the battery had been consistently in the 9100~9200 mAh range. But suddenly today, the total capacity lowered to 87xx mAh overnight. Anyone know the reason for this? Does that mean something's wrong with the battery?