I wanted to compare two batteries, 60v vs 72v by comparing their Wh, but I noticed that with 72v/20s it's 3.6*20=72v, unlike the 60v>3.6*16=57.6v .. so what's the right way to compare the Wh between 72v/20ah and 60v/20ah batteries, should it be 60v*20ah or 57.6v*20ah?