When I first got my MBA in June last year, it could do more than 10 hrs on one charge. Over the last week (or maybe two) that has dropped considerably. I have not updated the OS to Mavericks, nor downloaded a bunch of new apps. Only app I have running in the background is Box Sync. Just now, percentage dropped from 70% to 38% in just over one hour, just browsing on Firefox. Previously, this would not drop as fast. What gives?