What would happen if I was flying A to B, had an assistant at B with a spare battery, landed at B, had the assistant change the battery at B to allow the flight for returning to A?

Would depend on the distance,  if you were too far away as you land you'd loose contact with the drone and thus wouldn't be able to take off again,  if you were close enough or maybe still had unobstructed radio signal you could take off again.

DAFlys Posted at 10-20 00:12
Would depend on the distance,  if you were too far away as you land you'd loose contact with the drone and thus wouldn't be able to take off again,  if you were close enough or maybe still had unobstructed radio signal you could take off again.

We're assuming still in radio range, just ran out of battery. Imagine doing a flyover of a large tract of land and rather than RTH every time the battery ran out, there were 're-fueling' stations scattered throughout where one could make a pit stop for a fresh battery.

DKWatson Posted at 10-20 00:16
We're assuming still in radio range, just ran out of battery. Imagine doing a flyover of a large tract of land and rather than RTH every time the battery ran out, there were 're-fueling' stations scattered throughout where one could make a pit stop for a fresh battery.

As long as the radio will reach you can take off.

The main constraint would be the ability to maintain signal between the RC and the drone. If that condition were met, you would be able to re-launch the drone. You should, of course, be able to maintain VLOS with the drone on landing and take-off.