Approx 8kwh to charge from flat - correct.
As the battery is leased then who cares about whether it is better to charge when ever or at set SOC s.
If owning the battery then not letting get below 20% and not over charging above 80% are the optimum. Certainly (if owning the battery) don't charge until 6 bars have been used and then charge to 100% and occasionally leave until the charger fans cut out.(3.5 to 12 hours).
I've stuck the the 4 bars left before recharge (when I could) and charged to 100% after 4.5 years I believe I have lost 3%.
I believe but cannot prove, that letting the battery charger run on after the dash reaches 100% and turns off is when the battery balancing takes place which is key to maintaining a good battery and range. The variation before cut off is down to the state of the balance the batteries are in and the amount of balancing it requires. Also affected by the temperature the battery is at when charging.
Sod it I lease mine I'll do what I want and let Renault sort it latter. Unless then stop battery rental and the battery becomes mine. Then I will have wished I was more careful.