A U.S. firm (LaserMotive) has successfully demonstrated a laser that can recharge batteries on UAVs or ground based robots. Current range of the rechanrging laser is about a kilometer or so, but it opens up all sorts of possibilities for keeping battery powered robots at work longer. The basic problem is, as always, that you need a lot of energy to operate a long range laser (which has to burn its way through the atmosphere). This limits range, and the amount of energy you deliver. But the LaserMotive technology has shown that, for transferring energy, they have a working system despite those limitations.