How much energy your vehicle consumes while not in motion is completely dependent on a number of things. In a cold climate, it’s not “very very little”.
Here’s a thread on why you won’t actually get the displayed rated range even if you drive at the EPA assumption:
This is why you can't get 'rated range'
That being said, it’s been proven several times that you can get the same BMS reported nominal energy remaining at 100% SOC by taking the displayed rated miles multiplied by the EPA rating for your vehicle. For example, my displayed range at 100% SOC is 262. The EPA rating for the 85D is 290 Wh/rated mile. 262 * 290 = 75,980 Wh. BMS was reporting nominal energy remaining of 75.980 kWh. I’m not sure how you can claim this is unreliable when it’s matching exactly what BMS is reporting.
Edit: I should also note I was a “non-believer” before as well and thought trying to calculate the battery capacity from rated range was not accurate. Then I did the math, compared it to BMS reported values via the CAN bus, and they matched exactly. Several other people have done the same thing, and it matches exactly. Turns out my initial understanding was wrong, and I have no problem admitting that. Part of my flawed understanding was how much misinformation is out there.