Varies from phone to phone and with everything equal, here is my opinion with experiences with three different 920 devices.
I generally pull the plug off the charger at around 745 to leave for work and generally go to be at 11pm to 12am on weekdays.
My 1st phone with 5 emails with 1 running as items arrive and others in 30 min intervals, 3 background tasks (battery level, weather, locksider), bluetooth off, nfc off, sensitivity off. I would have to charge by 2 or 3 pm as the battery would drain constantly when idle. So i sent it back for an exchange.
2nd battery same set-up as I did a restore, but downloaded more apps. This includes whatsapp/skype which i think were battery drainers. Same, off charger 7:45am bed by 11pm-12am and this phone lasted throughout the day easily with perhaps 10-20% left every night. Same usage habits, same apps running, same settings as as I did a restore and did not due a clean refresh once i received this replacement. So I was happy with this performance. The phone actually lasted two full days for me one time as I did not do much on the phone one day and it drained only 17% in a 24 hour period and lasted through the day the next day as I went back to work with no charge in this period.
3rd phone - same as the 1st phone, would last me until 2 or 3pm and I would need a recharge. Add on a constant random reboot throughout the day as well so essentially this phone is worse.
Im gettinga 4th phone soon and hopefully it works like my 2nd phone. Some may ask why did i get rid of my 2nd phone, my first phone was a red one, i was sent a white one for use in the mean tiem and swap out once a red was available. When my red became available, i gave it to my niece who had issues with her phone, so i gave ot my nice and got another red and the phone ended not working well. My niece is now taking the 2nd phone and keeping and Im getting a 3rd Red. That is why, but I've experienced both types of battery performance, good and bad.