Is it wrong to fully charge your android phone in general to 100% will it hurt battery life? and is it also to drain your battery to below 20% will it also hurt the battery life?
As derived from this battery-related answer:
Li-ion batteries, unlike former battery technologies, do not need full discharges - actually, it's better if you don't let them drop below 40% (it's kind of like a sweet spot for batteries; you'll age your battery if you store it below 40%). It's also unhealthy for the battery to be left at 100%, that's why a number of phones (Nexus devices, to be exact) quickly drain the battery down to something like 98% or 95% after you unplug the charger.