I've got the same problem after some system update in June. All of the sudden battery started to discharge from 100% to 55% overnight (in 8 hours), with wifi, bluetooth and mobile data turned off. Phone temperature raised to 39-41 degree Celsius. Additionally, battery recharge was causing a reset of power consumption stats right after the cable was plugged in.
After 3 days of struggle the phone also reported no free space in internal storage. It turned out that almost 20 GB were eaten by the Media Storage app. I have cleared app data and, apart from gaining free space back, the power consumption got back to normal.
Unfortunately, data clearance on Media Storage caused all the default ringtones to disappear, so now I'm fighting to get them back (phone restart, suggested on many forums, doesn't do the trick).