I wonder what a comparable gasoline car would have consumed in fuel if idled with the passenger compartment heat on for an identical 12 hour period of time in the same ambient temperature.
Assuming, for comparison, a V6 Toyota Highlander, approximately 0.5 – 0.7 gallons of gasoline burned per hour at idle, or 6 - 8.4 gallons of fuel burned in total. Fuel tank capacity is 17.9 gallons, so about 30%-50% would be consumed in 12 hours.