The MY2012 and MY2013 EPA stickers make no mention of the total amount of energy required for a full charge of the battery, but the original format used for the MY2011 clearly shows that a full charge requires 12.9 kwh (in the "Charging Routines" table), which differs from the ~10.3 kwh that we know the MY2011 uses from the battery.
Also, math. We know that the MY2011 and MY2012 are rated at 36 kwh per 100 miles and 35 miles per charge. Multiply these two figures together and you get 12.6 kwh/charge -- close enough to 12.9 kwh to account for with rounding errors. So it's not only factoring battery-to-wheel energy.
And charging efficiency improvements could not explain the MY2013 MPGe increase because only the City MPGe changed. If charging efficiency was the root cause, the Highway MPGe would have increase proportionally as well.
Last edited by jsmay311; 07-19-2012 at 11:20 PM.