[andrewflnr]

For the traffic cam application, where people aren't trying to shoot it down, it would be pretty simple to switch it out regularly with one from a nearby charging station. You might even be able to use a balloon to take off a lot of the weight, so you can just use the rotors for altitude adjustment. You'd be slower, but would probably last a lot longer.

[sammyo]

I wonder if anyone is looking at a hydrogen balloon/drone hybrid. Small so it's not a Hindenburg bomb, lots of failsafe, but the power/lift ratios might give it a significant mission duration.