what an excellent idea. Now I understand, thank you. A recent roadtrip gives these stats:

198.44 Miles Driven

251.61 Rated Miles Used

308 Wh/Mile

Battery Used

88%

61.11 kWh

Avg Speed

62 MPH

so, the constant is calculating 4.117 rated miles per kWh, or 242.87 Wh/mile.

and while that’s all well and good, all I have to do is multiply the 61.11 by 0.88 to know that my usable battery is only 69.44Kwh. So....what does this data tell you?

What was your rated range at full charge at the time of this measurement?

In your latest Teslafi report I see 272 miles. However 251.61/0.88 = 285.9 miles.

If we use battery % then the accuracy of this test becomes +-0.5% however if we know the rated range, that brings it down to +-0.2% (plus the accuracy of the average consumption)

198.44*308 = 61.12kWh

61.12/0.88 = 69.45kWh

now let's add min max to check rounding errors. 308Wh/mile could be 307.5 - 308.5

and SoC % could be 88 to 88.99 (for some reason SoC is not rounded but truncated)

198.44*307.5/0.89 = 68.6kWh

198.44*308.5/0.88 = 69.6kWh

So your battery's capacity is somewhere between 68.6 and 69.6kWh. If you have the rated range at the time of the measurement, then this calculation could be more accurate.

The usable capacity of a brand new battery is 74.5kWh. So yours has around 6 - 7% degradation assuming the measurement and the BMS data was ok. A little on the high side. That is very similar to what Tesla Bjorn has on his Model 3P (69.8kWh). Most people are at around 4-5% degradation at this mileage.