I was looking for a way to power my 11" MBA when traveling (plane and airport / offices where I don't have easy access to an outlet). I checked out the hypermac and batterygeek options but these were pretty expensive. I found this energizer portable outlet that you can plug your wall adapter into directly. http://www.amazon.com/Energizer-Portable-Power-Outlet-ER-2dFLY/dp/B000TSAPGC For $44, I should be able to get an additional 2.5 hours of use (office, web, wifi). The only test I ran so far was with a fully charged MBA, and it stayed in this state while using it plugged into the energizer unit for ~2.5 hours. (I do run coolbook) Another benefit is that the device has 2 USB ports which could be used to charge other devices. Only weighs about 1 pound, so I can throw it into my laptop bag with the MBA "plugged in". The only major con I see is that it has no indicator to provide battery status. But I'll live with this. Anyway, this maybe worthwhile for some of you in similar situations.