[sbierwagen]

Depends on the method, but you can be sure that you're losing at least 10% to inductive/RF losses, and more typically 20%.

Reasonable for a phone, batshit insane for EV charging, which is why Magne Charge never took off. (http://en.wikipedia.org/wiki/Magne_Charge) 20% of 6 kW for every car, times millions of cars...