Have you noticed how the battery life on your Nexus 5 is not what it once was? We have certainly noticed it here at EyeOnMobility Headquarters. Battery life is great some days and others it is just plain awful. It turns out that a bug in Android 4.4.2 is causing the processor to run faster and drain the battery that much faster. The trigger is the camera application. When launched by the user or by another application (like Skype or any other that triggers the camera in the background), the mm-qcamera-daemon then causes the processor to run faster.
Google reports having found a fix for the “current high CPU reports on N5 due to mm-qcamera-daemon” issue and it should be included in the next maintenance release. That will presumably be Android 4.4.3 KitKat but the version number has yet to be confirmed.
Reports of this issue are not limited to the Nexus 5. Google recommends that users seeing that on other devices report it to their manufacturers for an appropriate fix:
I’d also like to note that instances of high CPU use of mm-qcamera-daemon on other devices besides the N5 need to be reported to their manufacturers – while those devices also use a Qualcomm chip for their camera processing (and thus have a mm-qcamera-daemon process), each has differences in their software and issues with them do not necessarily mean the N5 has the same problem, and vice versa.
There is no word yet on when Google will release its next maintenance release. Until then, Google recommends a reboot as a temporary fix to fix this Android 4.4.2 battery drain issue. You can check in Settings > Battery to see if mm-qcamera-daemon is active and chewing through your battery’s life. If it is, the reboot will address the issue until mm-qcamera-daemon is fired up once more.
Sources : Android Issue Tracker // Phandroid