I do often get 1-5 % drain overnight, which is fine by me, what I just don't get is how the same phone with the same apps being used the same way (and the phone is charged to same way) can the next night drop 15%, and then the next day the battery life can be shortened still further.
The issue with certain apps having the ability to stop the phone sleeping seems to be the main culprit but it's still a bit hit and miss for me, especially when battery life is so important. It really puts me off installing new apps when they can change the phone's behaviour like this, not mention other problems that can crop up when an app alters the main functions of the phone in the background.