Attached is my solution to this problem. It consists of a deep cycle marine battery and power inverter (and charger to charge the marine battery, not shown here).
At probably about 50 lbs., it's definitely not portable unless you have a car, but if you are based out of a car while travelling, or out of a fixed base camp (and don't need to fly to get to your base location), it's the ultimate solution. The capacity of this setup is about 4-5 times that of even the larger of the DroneMax products. It's also cheaper than the larger DroneMax, at about $250 in total.
I use this when I go on road trips where I'll be doing lots of camping, or just for general car camping.