If you can find out the type of aircraft you are flying on, as well as the airline....you can use this website to see if the seats have an electric port.
This website gives seat layouts as well as what is included in each seat, and where it is in the plane.
Hypermac batteries are external and can keep you running for quite some time without an outlet depending on the size you want... But I'm not too sure about their claims on battery life as I have the one for my iPad and it doesn't charge it back up as much as it's supposed to.
Try using Coolbook, it has added another hour to my battery life while watching movies on my 11.6. Probably the best app I have ever bought. http://www.coolbook.se/CoolBook.html