[Esel Mann]

Correct, the battery technology is one of the flies in the ointment. Simply not enough run time.

The other drawback is they need to be intelligent. Machine intelligence too is a ways off.

Additionally correct that their payload capabilities are limited. Hence in order to be practical it would be necessary to operate such in small groups each with it's own "specialty". For example one would possess the long-range comms link, another the video camera, another the acoustics, another the ability to say pick up/drop off small packages, another with the friggin laser beam,

Nonetheless, they are still cool!