There has been much recent work in quadcopters, self-assembling bees, and other types of small flying machines which require lightweight, long-lived power supplies. There is apparently no ready, tested, practical example of such a supply. "Nuclear" always comes to mind when considering lifespan, but "lightweight" does not usually come to mind when considering nuclear. I've read about atomic batteries, but have not found any good discussion of just how small they could be made, yet still be able to power our newest and smallest flying machines for long periods.
