I also found this on this websites forums. After some other tests, I'll try switching off LTE to see the results. Thanks to dkp23:
So I am currently on my 3rd Lumia 920 which I received last Thursday and the week I've used, the phone has been constantly draining. I got three apps running, two push emails and one 30 minute update. BT, NFC off and sensitvity on. Skype, whatsapp on my phone.
5-10 minutes of phone calls/day average
50-100 texts per day average
1-2 hours surfing internet (surf one hour straight during lunch in my car). This includes IE10, wpcentral, weave, people hub.
Weather updating every hour, locksider updating every hour, and battery status app running in background.
Off the charger at 745am and usually would be down to 10-20% by 2 or 3 pm, charge and then back down to the same by bed time at around 11-12 pm. The phone would drain 10% or more every hour on idle, so if i use, it drains even faster.
I was basically sick of this and am in the process of getting another exchange.
Now to the cause and the prevention part of the post.
Ok so, while I am using the phone, i noticed some funny things regarding the phone which included constant rebooting throughout the day, probably 2-5 per day. The 1st day, it would reboot almost every few minutes for awhile, very annoying. Anyway, the thing I noticed was when I put my phone to sleep after using it, when i turned it on to use it or to check something, i would see my reception bar at 0 bars or even have the no signal sign. I tried this throughout the week and most of the time, when i turn on the phone, it shows no signal sign again and after about 15-20 seconds, it will go to 4g (hspa) or LTE . I wondered if there was an issue with my phone trying to get signal while asleep, it seems the reception is very low while the phone is asleep which was causing my alarm clock to get feedback as the phone I think was struggling to maintain reception on LTE. My two previous phones, i didn't get feedback, but this one, would constantly cause feedback on my alarm clock to the point my GF was screaming at me at night. I also checked my email accounts setting right after i turn on the phone, some or all my accounts would have the red error "not up to date" sign on it, after a few minutes, it will sync and update. I've never seen this on my other phones. I live in a strong LTE area and my previous phones had no issue with LTE reception once provisoined, this phone, it would fluctuate back and forth on LTE and 4g all day. So I believe the battery drain is probably the phone trying to get signal while asleep and also trying to update your email accounts or facebook.twitter while asleep with the weak reception.
So i figured i just turn off 4g completely and do without LTE until i receive my new replacement and see how it works. So using the ##3282 code on my phone, i just set my phone to 3g constantly with no automatic network switch. Right now, off the charger at 7:45am, my phone is at 20% at 10pm here so my phone's battery performance has increased 7 hours by setting the network to 3g(hspa) only. So the issue for my phone and could be for others with idle battery drain is the phone switching struggling to maintain reception while asleep.
It is common knowledge LTE uses more battery, I understand that, but I have experienced a 920 phone with constant LTE and last me the whole day and even two days, but i had to give that phone away.
The point is, the idle drain issue could be the phone struggling to keep reception and when it does, it struggles to sync your accounts causing constant syncing efforts. This is not a permanent solution, there is no way I am keeping this phone, but for those waiting for a replacement, I would suggest changing the network settings to 3g only to extend your battery until your exchange comes in .
Also, since I've gotten this phone, there have been multple reboots every single day I've had it, since going straight 3g last night, I have had 0 random reboots.
This is just my experience so take it for what it is worth, felt this could be helpful for some