Battery fuel gauge, no learning needed on Nexus 5, should always be correct
Looking at the Nexus 5 service manual I found it was using a new type of fuel gauge from Maxim the MAX17048. This works differently to other types in that it doesn't measure coulombs (i.e. current in and current out), but works just by battery voltage. From the datasheet:
The ICs use the sophisticated Li+ battery-modeling algorithm ModelGauge to track the battery relative state-of-charge (SOC) continuously over widely varying charge and discharge conditions. The ModelGauge algorithm eliminates current-sense resistor and battery-learn cycles required in traditional fuel gauges. Temperature compensation is implemented using the system microcontroller.
Also this means while other types of battery monitor become less accurate over time and don't correct themselves until a certain event is seen, such as a complete discharge/recharge cycle, this newer system is suppose to become more accurate over time, and also is pretty accurate from the start as no 'learning' is required.
So there is never a need to fully discharge/recharge the battery in the Nexus 5 in order to correct any error in the battery charge monitor. This partners well with the wireless charging which can see lots of small top up charging.