I recently completed an experiment with my Lumia 920. It seemed as though the battery drained quite fast while the phone was asleep. It turns out it did and I found the cause...NFC.
This morning I was browsing through forums and found some people saying turning off NFC could boost the Lumia 920's battery life. And you won't believe the difference that has made.
Over the past few days when I listened to music, the phone drained more than it should. At around this time over the past few days, my phone would have drained down to around 35% or so.
Here is where my phone is now, with NFC turned off, and the same usage as the days before. I've listened to music for at least 3 hours while I have been working and made some calls, sent some texts, and looked up an article or two.
That's right, with moderate daily use my phone's batter is only at 82%. It may not seem impressive to some, but if you've been having battery drain issues, the difference is stunning. My battery can easily last a day, maybe even two at this rate, and I didn't even have to turn off WiFi or LTE once.
Turn off NFC by going to Settings >> Tap+Send >> NFC sharing - turn to Off