In trying to figure out what I owe my condo for electricity from the 120 VAC outlet near my parking space, I discovered that you cannot use measures of energy gained by the MS battery with a 85% efficiency factor. At the top end of the charging curve, for example, only one-third of the energy ended up in my battery over a 17hr session; the rest was wasted as heat. And that is with limiting current to 5A; at 7A, it is far worse. The charger just spills the excess rather than reducing the draw. A Kill-a-Watt power meter inline with the 120 VAC extension cord will do a better job, but even then you must correct for the voltage drop before it gets to the car. If you start charging from the 17" screen and watch the first voltage displayed (when it still says 0A), you will see it drop until amps settles down. The ratio Vo/Vload times the kWh reading on the meter tells you what you are really using by including the heat dissipated in the wiring. Anyone worked this out in better detail? Tesla really should document the power throughput for AC charging, to give us better guidance on avoiding wasted watts.