Hi folks, I got my 13" standard MBA 2 weeks ago and it has been wonderful except the battery only lasts 4 hours even when the screen is on half brightness. The timer fluctuates quite a bit from 3 hours to 7 and changes spontaneously even though I am not putting any extra strain on the battery. Has anyone else had this problem? My charger also over heats a lot and you can hear a lot of noise coming from it. What is the best way to wipe the macbook clean before I return it without doing a complete reinstall. All I have is a bunch of documents which I will erase, some programs that i can uninstall and then a bunch of saved passwords in safari. And is the exchange policy 2 weeks from delivery date or order date?