Charging power used to keep battery warm in winter
I have been logging the power used by my Voltec charging station to correlate energy used to maintain the battery temperature in the COLD Maine winter. It seems that the Volt needs to draw power of 1500 to 2500Watts (at 240V) for brief bursts of under 10 minutes fairly often when the temperatures drop below 20F. Below are some charts from my loggers so you can compare temperature with energy used to warn the battery. We did not drive the Volt for the last 2 days because it was snowbound by over 2ft of snow (storm Nemo). It's not a LOT of power, but a clear reminder that it is wise to leave the Volt plugged in.
You can see current charts on my Chevy Volt page: http://www.arttec.net/Chevy_Volt/index.htm
When we are driving in sub 20F weather, the engine generator comes on about 25% of the time with a dash warning: "ENGINE RUNNING DUE TO TEMPERATURE". According to my DashDAQ it is keeping the battery coolant above about 40F.