I'm using a mid 2013 11" MBA on Yosemite 10.10.5. I use it all day at work plugged into a thunderbolt screen. This morning when I was using it at home not plugged in the laptop shut down because the battery was down. At work it runs and shows that it is plugged in in the upper right display but after half a day it still shows 0% charged. The light on the power cable isn't lit to show it charging but its working so its obviously getting power. What's going on? Any suggestions?