I drive a B250e, (with 28 kWh battery) and it's my second winter season with the car.
It was -19F last Friday. Starting from my heated garage, and a full charge, I did a round trip to see a client. 22 miles each way / 44 miles total. Car sat for 3 hours outside (unplugged) before making the return trip. Pulling into my garage, the car indicated 20% charge remaining. I had the seat heater on the entire time, but was making conservative use of the heater; had it set at 72F but had it on ~ 50% of the time, mostly to keep the windows clear. It was a freeway drive at between 55-60 mph. Based on those conditions, I'm pegging total range at about 53 miles. As a comparison, at anything above 60F, I normally have over 100 miles available.
As a general rule of thumb, in extreme cold conditions, expect up to a 50% drop in range. Yeah, you can do pre-conditioning and other gimmies to mitigate the range loss it a little, but Siberia always takes it's toll.
2014 Mercedes B-Class Electric Drive
2012 VW Jetta Sportwagen (not-so-clean-diesel) TDI
2008 BMW X3 3.0 "Beatrice"
2004 BMW 330Xi Sedan
My 9.2kW DC Solar: https://easyview.auroravision.net/easyview/index.html?entityId=7466210