After doing a balance charge so the battery was at 100% and showing a range of 245 miles turning the AC on reduced the range of my car by 17 miles. The GOM would have based that reduction in mileage based on the total range, and because I had only just turned the AC on, the AC working flat out for the whole journey, which it obviously wouldn't.
17 miles of range at 3m/kWh or 5.6 kW, charging at home would cost me 54p.
245miles - 17miles = 228 miles
54p divided by 228 = 0.23p per mile
Put another way, having the AC/heating on means I can travel in a warm car that doesn't mist up for about a fifth of a penny per mile.
Guess what? My AC is on all the time ?