I'm not sure if it's ever been said but just to be sure:
This graph is why using a battery between 20% and 80% causes much less wear.
Especially below 10% and above 90% the voltage changes rapidly, until the safety kicks in to avoid total breakage. The less voltage difference, the less wear on the battery.
for the nerds: yes I'm using a specific li-ion graph as example but you'll find similar curves with most types of batteries, and less voltage change is almost always less wear.
