Maxing battery out shortens overall life and adds very little percent to run time. With all Lithium
batteries, 80-90 percent charge is recommended and any parasitic drain while charging damages the battery, shortening the usable life. In short, if it concerns you to replace
batteries prematurely (does not to myself) then do not overcharge or use while charging. Most of the older cheap chargers I have had do an improper CC (too high) charge and have completed cycle with as high a voltage as 4.25-4.55. This is bad. The better quality chargers charge with a proper CC/CV ratio and mine have never been above 4.09 - 4.17. If you really want to understand proper charging techniques go to battery U. Link was a few pages back but here it is again.
Charging Lithium-Ion Batteries