The car protects the battery with the famous anti brick 4kwh, then also it kinda wants to save 3,5-4kwh below 0 and anti brick.
My 2013 S85 has 75.1kwh useable energy and it is 3.8kwh below 0% and 71.3 from 100% to 0%
Now those 3.8 you kinda step around with a light right foot and dont tempt...