I monitor energy use intensively in my home, because I am a scientist/engineer and give seminars about my NetZero Energy home that produces enough solar and wind energy for heating/ac, hot water, all electrics and all Tesla driving (and it is cost effective...cheaper than paying for fosil fuel). I monitor energy use (kW) every second and live in a cold climate with an unheated garage.
I always keep my Tesla EVs plugged in at home as recommended. And I have noticed some differences.
Roaster: during summer the roaster topped off the charge every 24h BUT during the winter it topped off the charge more frequently to make up for energy use to keep its battery warm (above freezing).
Model S: during warm and cold weather it tops off charge (standard charge) ONLY once a day (Software version 4.0). But it keeps the battery above freezing on cold nights (when my garage is 0 to -20 F) hence in the AM when I want to drive away the range is reduced. NOTE: I keep my displays turned off as suggested by Tesla. Last night, however, I charged to MAX range and overnight when it was cold it topped off the charge every 60 to 90 mintues to keep the battery above freezing. THAT ISN'T GOOD BECAUSE REPEATED CHARGING TO MAX RANGE SHORTENS THE LIFE OF THE BATTERY.
I hope someone at Tesla Motors is reading this blog because I think they need to improve the charging software to work more like the Roadster, i.e. when it is cold (and the battery temperature drops below 32 F)it should top off the charge very frequently in standard range charging.
Also it would be helpful to have a feature that will allow owners to warm up the passengar space from the wall plug power. I figured out how to do this but there should be a simpler way. How I pre-warm the passenger space in winter: I noticed that the climate control comes on as soon as any passengar door is opened. So for now I open the open the rear passanger door then mostly close it (not latched). Then I set the charge rate to 10 A so that it will charge while it is heating.
I anyone (especially Tesla a engineer) wants proof of what I say, I will share my energy monitoring records to prove my statements above.
Prof Mel Tyree (email@example.com).