I've owned my 85kWh Model S for about 2 months, and have tried to monitor the number of miles driven and the energy used through-out this time. During this time, I've driven a bit over 3500 miles and have averaged about 295 Wh/mi. I've also been able to track the "vampire drain" at a fairly consistent level (approx. 0.33mi/hr or 8mi/day - some worse than other). What I'm having a hard time calculating is how much energy I'm actually pulling from my energy supplier (as I have to pay them for usage), vs what Tesla states the energy used for the miles driven is. Breaking it down a bit further, my battery usage for miles driven averages around 290 wh/mi often. But, if I factor in the vampire drain, I've been coming in at about 340 wh/mi. Roughly a 20% premium. Has anyone else figured out what the premium from this to the actual energy usage for charging the battery is? Thanks.