Todd,
I have convinced myself that the voltage and current reported during charging is reasonably accurate, within a few percent, and I doubt there are significant losses between the meter and the connector in my setup. I base that on having a Smart meter that gives me hourly consumption data from my electric supplier. I see between 230-240 V and 40 A, or 9200 to 9600 W on the charging dialog or in the app. The consumption seen on the BGE web site is always a bit under 10 kW if charging is continuous for more than an hour (since hourly averages are posted), when other loads are negligible (shutting off other big loads, such as heat pump, dryer, oven, etc.). So the electric company agrees well with the data presented in the car, and my billing is based on the electric company data. kWh into the car can be gotten from the power observed at the dialog and the duration of the charging, given by App notification start/stop times.
App notifications also give us battery SOC as rated range added, and that translates into kWh stored in the battery, knowing rated consumption (189 Wh/km for my MS). When I compare the reported energy at the connector as described above to the energy reported as being stored in the battery as described above, I get 91-92% rectifier efficiency. Others have reported values as low as 80-85%, but I don't get such low values with this method.
After looking at those numbers I'm generally satisfied that I'm being charged for a reasonable amount of electricity, and pleased to see such high charging efficiency. So, while it might be interesting to know just how much electricity goes to the car, I'm not motivated enough to invest in a separate meter, and I can get a good estimate by just tracking it on the trip meter and adding 10%.
