"usually" it's best to have lithium batteries sitting between 10-80%, that's when the cell is at its optimum performance and really is the sweet spot.
Below 10% for too long and you can get crystallisation of the lithium which in turn kills the cell.
However, as mobile generally only sit below 10% for a short while, there is generally not enough time for the degradation to occur, which leaves us with the upper region of 80%.
Again generally filling from 80-100% can cause heat build up within the cells which can also degrade the lithium, but with Sony batteries, the protection of adaptive charging means the heat build up is limited, and coupled with battery care means it's spending less time at this upper limit charge period.
So while "usually" 10-80% is optimal, charging from empty to full with Xperia should give many more years of battery lifespan Vs many others without such features.
