This is also incorrect. All modern phone batteries have a PCM (Actually they use a BMS, a more robust sysem than PCM. I use PCM's in other equipment myself so I was biased to this type of battery protection) so they CANNOT be fully discharged no matter how hard you try. You can bring your phone battery to 1% or dead and the phone actually still has plenty of juice left, the PCM just keeps that charge so the phone cant brick the battery. The best practice is to keep your phone battery between 15-60%, you'll get close to 900% charging efficiency vs. charging to 100% (which is 100% efficiency) or charging to 85% (200% efficient) at least according to the battery tracking software accubattery I've been using for the past year.