You don't need to fully discharge a modern lithium ion battery before recharge, that's a leftover from the first nickel cadmium NiCd rechargeable batteries that used to suffer from "memory effect". If you didn't discharge them and say set the recharge off at 25% then over time the capacity would drop as "0%" got effectively higher and higher up the original scale.
Most advice I've seen and used is to recharge at 20% or so and let the device do the rest. If you use the official charger and cables it will optimise the charging, most slow down over the last 10% for example.
The % meter is only a best guess by the gadget based on the last few charge cycles anyway.