i own a macbook air 2012 13", (bought it in november 2012)my battery monitor shows my battery is at 4611 mah max capacity now, out of 6700 when i first bought it. it says to replace the battery. but i'll do it in the near future, not right now. i like to charge my ipad or iphone, or external mini battery charger, or camera (point and shoot or gopro) through the usb. when i do charge it, i make sure my macbook air is connected to the wall socket for power. i'm wondering, does charging electronics through the usb port affect battery life in the long run? or does it have no effect?