Update: using TeslaFi I determined that there is a difference between charging energy to the battery and charging energy used. I am measuring 78.5 kWh charging capacity to the charger but only 73.5 kWh actual battery charging capacity.
After updating to 2019.5.15 and observing a range increase from 307.5 to 314.5 miles on my LR RWD Aug 2018 M3, I decided to make an accurate measurement of the usable (effective) battery size based on the amount of energy needed to charge battery. If someone has good data on the previous size or can run the same measurement pre 2019.5.15 upgrade, then we will know if Tesla unlocked some battery capacity (in addition to any possible efficiency or multiplier increase).
Result: 78.5 kWh battery charging capacity = 7.85 kWh energy into battery / 10.0% SOC change
I charged from exactly 60.0% SOC to exactly 70.0% SOC, I know this because I used Tesla's energy app to make sure I stopped and started at those levels. You cannot just use the main SOC display, resolution is only 1%. Tesla rounds the number so 60% could be as low as 59.5%). For example, when I set the SOC charge target to 90.0% it is typically 89.6% when I measure it using the energy app right after charging.
I know exactly how much energy I put into the battery because I measured the charging power at the battery in 5 min increments (e.g. 240 V * 32 A = 7.68 kW) using Tesla's charging app, and recorded the time to charge from 60.0 to 70.0% using a stopwatch (00:60:25).
I tried to validate this result by measuring accurately the energy used to drive 10% SOC, but I don't have the TeslaFi app and using the energy meter is inaccurate. If someone can do this, i.e. capture kWh used in x.xx kWh resolution to drive 70.0-60.0% that would be awesome. I measured 75 kWh effective usable battery based on using 3.0 kWh to drive 4.0% SOC change, but I think it is not precise, I was eyeballing the SOC using the energy app.