[Q] Sudden battery drain topic

I've had this phone for about a week and this is the first instance where my phone has gone down to 10% battery in the matter in 8 hours with what I can only describe is light use. I get a few emails, most of the time it sits with the screen off. I checked the battery stats and saw Android OS at 21% usage followed by Cell Standby and Screen.

I am rooted at 5.0.1 but stock and encrypted. Only mods I have done is DPI at 493 and double tap to wake.

Anyone else experienced this before?