Even if your laptop battery lasts the entire flight, you must hunt for a socket to recharge it once you get off the plane. The same goes for the cell phone. And if you forget to recharge the cell phone overnight, the next day can be hit-or-miss outside the hotel room.
Consider the N-Charge battery from Valence Technology. At two pounds and roughly the size of a thick clipboard, the N-Charge is an external battery that dispenses power when you’re away from the plug.
Even though the batteries start at $350, a bit expensive, it might be worth it for those who hate to worry about running out of juice. More here.