Plus, I bet the last 5 miles of the 40 are like a golf cart going up a hill to the clubhouse after finishing the 18th hole.
No. Charge state and whether the generator is running or not has no affect on vehicle performance. The motor/inverter is the limiting factor, not the battery pack. The small depth of discharge used means there’s little voltage drop over the cycle, and the high power output of the type of cells they’re using would sustain it even with a high depth of discharge.