I would like to suggest that you buy a power pack, you can get some from many different websites. one i have is from xantrex,
www.xantrex.com. The one i have will supply 300 watts of power for a while, like 3 hours i think. It would easily power a laptop charger for 6 hours. They sell the 300 watt for around $80 I got mine from where i work (MENARDS) and it only cost me about $65. They xantrex does have more powerful verisons that would last longer and power more stuff. But these you would have to ship down with your robot or with someone driving if you were to be flying, i dont think the airport would like to see this large electronic device getting put onto the plane.