so my brand new 13" macbook air arrived last tuesday. over the last few days i've noticed that i only get 2-3 hours of battery life even with the screen brightness nearly all the way down. right now, i have 79% battery life remaining and it only says 2 hours 24 min left. I've only used it for about 30 minutes this morning and it was fully charged. i'm about ready to return it, this is extremely disappointing. anyone else having this issue???