On my 2010 MBA 11" I bumped up the power socket independent time to 26 hours with the use of an external 150Wh battery. I found a great product that really works with all my different MacBooks, iPhones, and iPads. The external batteries come in four different capacities: 60 Wh, 100 Wh, 150 Wh and 222 WH. I carry the battery in my notebook bag / backpack where it charges iPhone/iPad and MBA or MBP. It is available from hyper shop, see http://www.hypershop.com/HyperJuice-External-Battery-for-MacBook-iPad-iPhone-USB-s/91.htm I am very happy with this battery and I am using it since 4 months. Who also has experience with this product or alternative battery packs?