Why is my battery draining when shut off and plugged in?

[AC Question]

Two days ago I woke up with my phone plugged in from a full nights charge at 90%. Battery proceeded to drain quickly throughout the day even while plugged in. I've erased the last few app updates and used the factory reset function within the phone itself. I've even purchased a second battery and the problem still occurs. Yesterday I plugged the phone in with the new battery installed while turned off. I started charging with 45% when I checked a few hours later it was down to 37%.

 

[espacepublishing]

Try opening Settings -> Power Management. Then check "App power consumption" and "Battery Usage". These should give a good indication of what's consuming the battery.