A half depleted battery has several paths for the electrons to take so will fill the needs of the motor more efficiently.
A fully charged battery had fewer pathways for the electrons.
Its why going from 80 to 100% percent takes longer.
Best analogy is a car park with 100 spaces and 100 cars. The cars look for a parking space, as the car park fills up the last 20 cars have to travel around the park trying to find a space.
In reality there will be no noticeable difference for the motor, until the battery gets close to depletion.