The Mountain View have closed a bug in Android 4.4.2 about Nexus 5 with the launch of the camera, either in the background or by third-party applications (Skype or Tango) creates a process that kept the CPU to the maximum, with the consequent excessive energy consumption.
As we can read in official channel of Android, this problem problems It has already been fixed and probably this solution is integrated in a future update of Android.
Google has only confirmed that bug in 4.4.2 Android on Nexus 5 by which we cannot confirm if it will affect other companies, HTC, LG and Samsung handsets.
If you have checked that the mm-qcamera-daemon service consumes much battery time, your terminal is undergoing this bug. In theory with a restart should be fixed temporarily but you already confirm that Google has put an end to this problem and that the solution will definitely arrive in the next update of the OS.