Beware of Calibration Issues
Professor Foxcat has provided some evidence that the batteries are better kept at 80% maximum and 20% minimum. One caveat is that we don't know the actual calibration of what the phone calls 100% and 0%.
For instance, my Chevy Volt reports the number of miles, so in summer, when at full charge it says 41 miles. When it gets to 0 miles, I'm told it is actually at 15% of the remaining charge. I've read that will prevent electrical problems with the battery of some sort or other, which could cause serious harm to the battery.
Therefore, Moto might have the charger to indicate 0% left in the same way, when the battery is physically at 15%. In the same way, who's to say that they call 100% the physical maximum? If 80% would result in more battery life and even perhaps more safe operation, my guess is that they would stop charging and call it 100% at whatever level is best.
So I would not set an alarm to disconnect my phone at 80% or power it down at 20% without being sure of the top and bottom calibration limits. If they already have set 20% as what is reported as 0% and 80% as what is reported as 100%, then you'll actually be stopping the charging process at 64% (80% charged x 80% max) and powering down at 36% (100% minus 80% discharged x 80% discharged min). My math might not be correct but you get the idea.
