Okay, here are my statistics. Brand new Lumia 920, came with Portico update, battery charged only after draining completely.
1st charge: lasts 9-10 hours with light-moderate use. Heating. (I get frustrated and google the problem, which leads me here.)
2nd charge: lasts 9-10 hours with light-moderate use. Heating. (Even more frustrated, but read also about that the Lithium battery needs a few charge cycles before getting optimal.)
3rd charge: lasts 6-7 hours with internet sharing turned on constantly. Heating. (Understandable)
4th charge: After 8 hours of light-moderate use, even internet sharing for 30 minutes, the battery is on 72%. (I'm relieved and happy for my new Lumia 920!)
I didn't do any "magic" settings or resets, I have 3 mail accounts pushing mails. NFC on or off doesn't make a difference.