Resurrecting this old thread as my experience should help current (and future) owners of (not just) the 920 to avoid shelling out for fast chargers/charge only cables etc (as I did).
I am very set in my ways and don't materially change either my app list or my start screen for months. I recently decided to try a new battery app (looked very nice compared to the stock one I was using before).
I also use my 920 as my main navigation device and went on a business trip a couple of days later. I have been using for more than a year now a Nokia DC-20 (1A output per port) with a charge only cable taken from this kit:
Fast car charger with cables and clips - TomTom and it has been more than sufficient (apart from Drive+ and Bluetooth I have x3 email accounts on push, Amazing Weather HD, BBC News and the battery app running in the background) .
After a couple of hours on the motorway I saw the battery icon on screen for the first time in ages actually go down (normally the charger/cable combo keeps up with the drain and even goes up by a bit). Upon arrival to my first stop battery was down to 75%! After the second stint the battery continued to drain and after about half an hour it was down to about 65%. For the return trip changed the battery app back to the original and low and behold normal operation resumed.
Lessons learnt:
1) The majority (if not all) of incidents of abnormal battery drain are down to badly coded apps. WP8 on its own is as battery friendly as it gets.
2) Before going out and buying fast chargers etc look at your app list and start the elimination process until
3) 8.1 arrives with its builtin individual app battery drain indicator (if the SDK is to be believed) which will separate the men from the boys (apologies to the ladies, just a figure of speech).