The lithium ion battery does not need to be drained fully, as it doesn't develop a memory as did with older NiCad (Nickel cadmium) batteries. Google or read article below. http://www.batteryuniversity.com/learn/archive/memory_myth_or_fact
Draining the battery fully and recharging will cause more heat and in time shorten the lifespan of the battery. There has been much written about wireless charging causing the battery to heat up more during charging and likewise not good for the battery.
The V20 was suppose to have wireless charging capability but is not activated or not sure about it because I know my Verizon V20 charge light will change to red on the charger but the battery icon doesn't change on the phone?