I got a 2020 about a year ago, just over 10K miles driven so far. Battery has been gently treated, only above 85% a few times for a few planned trips.
I fully charged the car and took a 210 mile round trip, speeds generally just under 70 except a few times in construction zones or traffic dropped to 50-60. Less than 10 miles on surface streets. Climate control was set for ventilation only, no A/C or heat. Exterior temps ranged from low 70's to low 60's.
After 210 miles I reached home, display showed 53.6 kWh consumed over 209.8 miles, so .255 kWh/mile or 3.91 mi/kWh which I think was pretty good. The summary showed 100% to Driving and Accessories, 0% to Climate, and 0% to Battery conditioning.
Next day, I drove an additional 24 miles to see what would happen as the battery ran down
First indication was that the battery indicator bars turned orange
Next indication occurred at about 61 kWh consumed, propulsion was limited (although still plenty for freeway driving)
Next indication was the battery indicator started flashing and mileage remaining showed as "LO"
At this point I reached my home and turned on the heater full blast with windows open. Consumption was 5-6 kW to the heater and to the idling car. I went forward and backward in my driveway so i could see whether the car would still move, and it did, (propulsion limited of course)
With about 63 kWh consumed the final bar stopped flashing and went out, but the car would still drive, at least at driveway speeds.
Finally, with 63.2 kWh consumed the car shut down suddenly and the display read "Out of energy. Charge vehicle now!"
So my takeaways were:
Car gives a fair bit of warning, but when it finally has had enough, it seems to just quit. I don't know whether it would have been different if I'd been traveling down a road, but in my driveway it felt I had been given adequate warning.
My usable capacity is 63.2 kWh at moderate temperatures. Based on my consumption (highway speed and ventilation but no AC or heat) that would have taken me 247 miles, pretty close, I think, to the EPA rated 259 miles and this was at least 90% on the highway.
While the rated usable battery capacity is 66 kWh, some users have reported slightly less. But even assuming 66 is the real number when new, my battery has lost only between 4% and 5% of its original capacity over a year and 10K miles
Had I driven slower, then obviously I would have gotten more miles. But I believe I would also have gotten more kWh out of the battery. I know there has been discussion here with some maintaining that kWh is independent of speed, but I'm quite certain it's not. The faster you go, the more current is drawn from the battery and, due to the internal ESR of the battery, the more energy is converted to heat inside the battery and therefore not available for use. So slower not only uses less energy but allows the battery to supply more energy. How much? I have no idea, but some. This will also depend on the temperature and battery state of charge (low temp and/or low SOC cause higher ESR)
Hope this is helpful