Hi! I am new at this so looking for an expert to explain the following. I have a 2015 Leaf so rated for 84 miles or 135 kms. Going to work and back is economical i.e around an average of 8.8 kms/kwh. If the usable battery is 21.3 kw/h (my research suggested from 21.3 to 22.4, not sure which...