perhaps superfluous extra info
I was going to answer in a similar vein ... so herewith my thoughts in full
for scrutiny
I get 8kWh, which I suspect is a slight rounding u
looking at a representative charging sample in TeslaFi:
Charge: 7 Hours 8 Minutes
Start - 29 %, End - 90 %
Used - 54.0 kWh
Added - 48.34 kWh
Efficiency 89.5 %
I make that: 7.57 kW drawn, 6.78 kW at the battery
My home charger efficiency varies quite a bit (why is that? 99% of my charging at home is when I'm tucked up in bed!) from 85% - 90%, whereas work is consistent at 90% (3-phase supply, but charger is on one phase). Both sites are within a few yards of the supply.
The couple of times I had to charge from very-low to pretty-full I made a note for how long the car took to charge. For my P90D that worked out at 1.2 hours per 10%, and thus within E7 cheap-rate I can charge about 60%. But ... I leave for work at 6AM (E7 starts at 1AM in Summer ...) so if battery is below 50% I need to consider overriding scheduled-charge to start earlier.
If not leaving at 6AM then the scheduled charge can start at normal E7 time, and then it will continue, in the morning, until completion.
Having done all that maths, just the once!, I came up with:
If leaving at 6AM and the battery is below 50% then start a charge at supper time - 8:30 PM would be fine in Summer, and 9:30 PM in Winter, earlier just means I pay the higher rate for a bit longer, but for the number of times I do this in a year its trivial.
If I need 100% at 6AM then do that if battery is below 60%
If the battery is below, say, 20% then check the maths to make sure its starting early enough!! ... but ... in practice if I came home below 20% I would put the car on charge immediately, just in case I had to go out again.