Re: Does your battery drain from 100-90% very quickly, then from 90% down more slowly?
typical battery issue that`a 1 year device would face but surprised to see that happen to new HTC One.
have you been careless with the battery like charging it overnight, charge too often etc?
Charging a battery overnight doesn't cause any problems as the voltage regulator stops the charge when needed and charges when needed to keep the battery full. Lithium Polymer batteries do not create a memory effect so charging often doesn't harm the battery either.
The OP hasn't stated what he has running in the background to make it do that. On the charger over night, the phone goes to deep sleep. When taking the phone off the charger, it wakes it up waking all it's sync features....such as google, facebook, lookout, twitter, and the plethora of syncing apps sucking down juice as soon as they connect. That would make it drain a few % in just a few minutes. If he nothing like that syncing, then I would drain the batt down to 5% or less.....do not let it die....turn the phone off and charge till full. Do this a couple times and it will recalibrate the battery.
On a side note, my phone has a few apps that sync as soon as I take it off the charger, I will drop 2 to 3% within just a couple minutes then it tapers off to normal.
Nussin' to worry bout' my homies.