3 years ago when I first got my 2011, I charged at 120 volts for 2 months or so because I was getting ready to move (move was required due to owner wanting to sell) and did not want to put anything in there.
So I was using the Kill a Watt meter and found that I was averaging right around 75% "well to wheels" efficiency using the miles/ kwh meter on the dash of the LEAF for my "battery to wheels" numbers. This in essence measures charging losses only since there is loss in every step of energy transfer process and yes, this banks on the dash calculation being accurate and that in itself is dicey but at least its not Carwings! :)
After the move and getting settled in, I was investigating 240 volt meters and found nothing in the range I was willing to pay for until Tom Saxton a Pacific Northwest EV enthusiast turned me onto his method which was to simply to install my own meter!
I started by going online to http://www.hialeahmeter.com/ then mousing over "products" at the top of the page and clicking on single phase remanufactured meters in the drop down menu. There I selected the "EZ Read FM2S 200A 240V 3W Meter" which was $17.50. This meter requires a base plate which was another $10.50. Shipping/taxes, etc. added another $15 so $$ invested; $43.45
Went to store to purchase some random parts for another $11 and simply disconnected my plug, installed the meter, and then ran wire from the meter to a new plug box.