This is helpful. I still ended up with 10% range loss from the time I parked the car yesterday afternoon till the time I got to work 10 miles away this morning when the snowflake icon was gone.
As others have indicated, the snowflake makes things difficult to determine, exactly, for a single overnight period. I think the best way to determine approximately how much vampire drain you have is to look at your wall-to-wheels efficiency for the period, assuming you have a way to meter that (either at home or using a Chargepoint or Supercharger). It's really all that matters, as you say. It won't be as precise, but probably the only way to determine about how many % you really lost due to vampire. You still have to make some assumptions about charger/battery charging heating efficiency (seems to be 87-90% if you're not using a Supercharger - so potentially that slop might create large error on your vampire drain number), so it won't be precise, but in cold weather conditions I think it is really difficult to come up with a clear number unless you look at your efficiency for a full cycle. Obviously also includes heating losses, etc., but you can monitor that on the in-car display assuming you don't do any significant heating of the vehicle while it's parked (the in-car display does not count any energy you use while you are parked).
Some of the apps track the miles/energy added but you have to be careful to distinguish between miles/kWh added to the pack and kWh drawn from the wall. (Which are different by about 10-13%.)
Assuming you charge to the same %/miles as the prior charge, and you're not using a supercharger:
Total kWh added (measured at the wall) = (Miles Since Last Charge * kWh/mi since Last charge + Parked Heating & Other losses (not quantifiable) + Vampire losses (in kWh) )/0.87
Again the 0.87 is approximate and is closer to 1.0 (I don't know what it is, it is less than 1.0) for a Supercharger. But you can solve this formula for Vampire losses to get a rough idea. Obviously if you have non-quantified losses then you can't solve it.
Personally, I have seen an instance about 10 days ago on version 50.6 where I inexplicably lost 10-14 miles in a very short period of time, but then soon thereafter, I came back to the car after leaving it overnight unplugged and it had 7 miles MORE than when I left it (this is the only time I have ever seen the miles go up). And this was NOT in cold conditions or with a snowflake. So, the "roundtrip" monitoring is really the only way to go.
Monitoring the true energy content of a battery accurately is really, really hard to do over a huge range of temperatures & SoC. That's one of the ways to explain this bizarre behavior of the rated miles display (in addition to just simple software bugs).
I would expect 4 miles per day of vampire drain (assuming about 1 hour of driving per day). That's what I have seen quite consistently over a long period of time. It's been briefly worse when I've left a door or trunk open or whatever, and generally seems slightly worse than that (5 miles per day?) on version 50.6.
Lifetime, I would estimate about 10-15% of my energy usage is vampire drain. I get about 30kWh/100miles (300Wh/mi batt-to-wheels) when driving the P3D+, and my wall-to-wheel energy use is closer to 38kWh/100miles, lifetime.
We heard this and tested it in the snow last Wednesday. In our tests, the FLIR didn't show the cameras were heated while the car was just sitting outside in the snow.
I've found that the parking sensors are sometimes on and sometimes off with my FLIR. I haven't gone back to experiment to try to determine the pattern - but I wonder whether it depends on whether it is light or dark. And I've never seen the cameras heated in the FLIR. But I'm not in a location where they would need to be heated.
Yes, EVs are less efficient in the cold, as are ICE vehicles. EVs take a bigger hit because they're starting from a higher efficiency 'standard' and they don't give off oodles of waste heat with which to heat the cabin & battery.
