[Tony K]

Tesla battery life in a traffic jam in winter - you'll be fine in the vast majority of cases, aside from truly extreme temps, if you have a decent charge to start. A Model Y with the heat pump at full charge in the VA mess would last 36 hours. The Model X with the resistive heater would last 28 hours. Those numbers were based on maintaining a 70 F internal cabin temp and using the seat heaters. This video was done in Michigan.

 

[Tony K]

Yeah, but how many of those would realistically been at "full charge"? Even at half charge, that would still give plenty of sustained heat for the duration many were stuck in traffic although you might be cutting at close with the Model X - some were "stuck" for over 20 hours. Plus, one could extend it by only running the heat as needed - maybe 10-15 minutes every hour. Whenever I have been stuck in such conditions (rare), I would only run the engine long enough to get the cab warm and then shut it off.

In the video, after 12 hours, they ratcheted the Model Y down to 60 degrees, and based on the results at 18 hours, they'd did the math, and figured they would be good for 2.5 days in the Y at full charge.