Submitted by Bighorn on December 5, 2013
Yesterday, when it was 0F, I attempted to pre-warm the battery by starting a charge about 2 hours before departure. The garage was about 38 degrees and the 60% full battery was very slow to accept a charge, maxing out at 4 of a possible 12 MPH. Driving to work, it took a good while for my energy usage to drop below 500 Wh/m though it eventually dropped to about 480 Wh/m after 10 miles, with regen limitations the entire way
So I decided to try a trickle charge technique where I charged at 8 MPH for the 14 hours before my morning departure. I also preheated the cabin about 15 minutes ahead of time. Mind you today it was -15F. There were no limits (dotted-line) on power output or regen. After 5 miles of driving, my average use was 206 Wh/m. I had the seat heat on, but climate off. It was at this point I needed to use the front defroster because it was fogging up, though comfortable. Over the next 5 miles, my avg consumption rose to 270 Wh/m. Because this commute involves about a 400 ft loss in altitude, it's not unusual to make it in under 200 Wh/m. Other confounding factors included icy buildup on the road that raised rolling resistance which also lowered the average speed by between 5 and 15 MPH.
I never considered charging while at work because I don't need the miles added, but considering the great loss in efficiency from a cold/unconditioned battery, it might be a good idea.