My approach lately has been to keep one of the car's timers configured to a five hour window (1:00-6:00 AM) and not charge every night; if I refrain from plugging in until I'm at 30% or less, then it never goes much past 80%.
On the other hand, if planning to make a significant drive the next day, I plug in regardless of what the state of charge is. Because if it gets up to say 95% that next morning but I'm about to go a hundred miles, then the battery is not going to be in a high charge state for very long so I don't worry about it. In general I treat the 80% number more like a guideline than an actual rule, arrrrr.
Welcome to the forum.
edit - I just realized you are talking about a 40kwh battery, so my numbers would be off for you. Maybe a 3 hour charge timer would be a better starting point, if charging at 6.6kw.