I gave my MBA it's first full charge and at 100% I have an estimated 8hours 52 mins usage left. Nothing open except Safari and browsing facebook and Macrumours. I have a base 13" with brightness set at middle. Not doing anything demanding, yet the battery life is a far cry from 12 hours. Also, I appear to be losing 1% every 5 minutes through light web browsing (no flash). Is this normal after one charge? or should I change it? Also, how would I be able to tell whether the model I have is a 2013, and not a last remaining 2012??