Regen goes to zero somewhere around -10C fully cold soaked. I'm not sure of the exact number (I mostly preheat these days).
How long the car retains heat after charging or driving depends on the temperature the pack started at (which we don't know because Tesla annoyingly doesn't report it), ambient temperature, and other weather factors. A very windy day will chill out the car much faster (it won't get any colder than ambient... it'll just get there much faster). Parking in your garage could slow it down substantially, due to both sheltering the car from wind and the fact that temperatures are often a little warmer than outdoor ambient.
Preheating the pack will give you 30-40 kW regen power. Getting full regen requires driving the car, and you may never get it in extreme temperatures. (Note that even when the yellow line disappears you may still have a small regen reduction, e.g. 50 kW instead of 60.)
Unlike the Roadster a 100% charge does not give you zero regen. You still have something like 10 kW, which makes a huge difference to the feel of the car. At 0 kW regen the thing glides so much you might think it's accelerating for a moment!
Regen will completely disable when the BATTERY PACK (And I stress BATTERY PACK) Drops BELOW 32*F Or Freezing. Now, due to the mass, and heat from charging etc..., charging could be done at 3 am and you might still have SOME*** Regen at 8 am or 10 am (depends on how cold it really is).
This is from a Technical Standpoint with Lithium Batteries.
When a lithium battery is below freezing, charging it actually Electroplates the inside of the battery, causing permanent capacity loss. THIS is why the regen limit is so important. I've had the car tell me Regen is disabled at temps as high as 25 degrees (remember, I stressed BATTERY PACK must be below freezing, ambient temps will only affect how quickly that pack gets their).
Now, when It was -30 out with a -50somthing windchill the other night, after having a fully warmed car, with no regen or accel limits, it only took about 15 minutes of being parked for it to drop from 60 to 10kw regen. At that point, even with range mode selected, the pack warmer kicked in. That increased regen (VERY VERY SLOWLY) and at the same time, VERY QUICKLY Dropped my range/rated miles. Plugged it in to a 14-50.
The 14-50 did keep up with letting the car charge (SLOWLY) while still drawing it's power for pack heating. Now, Pre-Heating the car, wanted more then the outlet could provide.
Pre Heating a cold soaked car, required what I calculate out to is about 50 amps at 240. So heater kicked in, as well as pack warmer. It was the pack warmer that pushed it over the edge. Though, raising the temperature of a car to a temperature that was 120*F WARMER then the outside, usually does require a good amount of power
And with that, Tonight's entertainment.
And for the record, #1, Yes, I know I need to Comb my hair, #2, Yes, I know I need a Hair Cut, #3, at -30*F I didn't give a damn about my freaking hair, I was more concerned with my genitals freezing to my leg. Oh, and Thank You TESLA for placing the heated seat heating elements in the perfect spots. That corrected the frozen genital issue; Grazie!!!
