I finally got around to this.
Test: I left home with 33% SoC reported on the display and arrived at the DCFC just as the car display turned to 31%
Battery Temp 74 - 77F
Charging was stopped by the car at 80% (Newb mistake, I meant to charge up to 81% for easy arithmetic but I forgot to change the max charge setting to 100%.)
Total charging time: 14 minutes
Max ~ 40 kW, down to 17 kW at 80% SoC
Battery resistance test pending ..
Major Newbie mistake: the car was running during test, as well as AC -- albeit at a low power.
End of test battery temp: 84 - 87F
9.16 kWh pulled from the charger. I'm not sure if the metered kWh is before or after the chargers. I *think* that DCFC tend to report kWh to car, so after the charger losses but this strikes me as a convention rather than engineering. I have emailed the chief programmer of the network this question.
9.16 kWh/0.49 SoC change = 18.7 kWh for 100% usable capacity (minus whatever energy was eaten by the car during the charging.)
LeafSpy reported 55.65 Ahr last week, so at a nominal 360 Volts I can expect 20 kWh of capacity.
Discussion: these two methods correspond quite well since the LeafSpy Ahr reading includes the unused anti-brick reserve.
1. The obvious -- next time the car is off
2. Hysteresis ignored
3. Battery resistance ignored
Why bother ?
Well, I like confirming that LeafSpy is giving me good capacity information; but more importantly to confirm that a simple charge test will substitute for LeafSpy if that method is not available or it has been compromised by a battery reset.