Using the EPA efficiency stats for the Model S, you can derive the charging efficiency. If you do the simple math of calculating the Wh/mi by dividing the battery size by the range, you get 288 Wh/mi for the 60 kWh and 321 Wh/mi for the 85 kWh. Those figures make sense, and if you drive relatively conservatively you'll make those numbers in the real world. When you look at the kWh/mi figures, on the surface things look a bit wacky. For the 60 kWh they calculate 35 kWh/mi (350 Wh/mi) and for the 85 kWh it's 38 kWh/mi (380 Wh/mi). However, those figures are calculated wall-to-wheel, which accounts for efficiency losses in the A/C to D/C conversion. By dividing the calculated the battery capacity Wh/mi by the EPA wall-to-wheel Wh/mi consumption, you can derive the charging efficiency. For the 60 kWh we get an efficiency of 82.4% and for the 85 kWh it is 84.4%. I have my doubts as to whether or not one vehicle is really more efficient at charging than the other, as the charging components of the vehicles aren't any different. The difference is likely due to rounding the calculations to the nearest kWh/100 miles instead of going out one decimal place (or calculating in Wh/mi). If the wall-to-wheel Wh/mi of the 60 is more like 345 Wh/mi and that of the 85 is 384 Wh/mi, you'd only have a difference of around 0.1%, and their charging efficiencies would be around 83%. If you want to use this to estimate your wall-to-wheel energy consumption, just take your driving kWh consumption from your trip meter and divide it by 0.83. I would imagine the EPA tests were performed using single-charger configurations with the mobile connector. From what I've read, using the HPWC with dual chargers has less overhead and is a bit more efficient. If you have dual charges and a HPWC, you're likely getting slightly better MPGe than what's on the sticker. Has anyone out there put a meter on their charger to calculate the real-life efficiency? If so, how does it compare to the 83% EPA efficiency?