A lot of people have been complaining about their battery discharging a little too fast on the Nexus 5 ever since the 4.4.2 update. It appears the culprit is the camera, and more specifically mm-qcamera-daemon. It causes the CPU to run more than needed, which subsequently causes the battery to drain quicker. It seems as if other third party apps like Skype is accessing the camera too often. However, the problem isn’t with Skype or other third party apps. It’s something Google needs to fix.
If you have noticed your battery draining quicker than normal, you can head over to Settings/Battery and see if mm-qcamera-daemon is listed. Unfortunately there really isn’t anything you can do to alleviate the situation other than doing a reboot, which is basically like taking an aspirin since the issue will come back. You can also look to uninstall any apps that utilize the camera, but then again, if you make use of those apps a lot, that might be difficult.