My little brother has a 2012 13" MBA. Recently I've noticed that the battery meter in the upper right hand corner is inaccurate. It takes forever to go from 100% to 99%, and when it finally changes to 99%, it's still not an accurate read. For example, right now the meter says 99%, but iStat says 94% - iStat seems to be more accurate than the actual meter! Any idea why this is happening?