I just completed a round of tests on my phone with all Background tasks enabled/disabled. The difference was 4% over 8 hours, or 0.5% per hour. Repeated the test three times with nearly the same result. Apps: USA Today, Fox News, Weather Channel, Mehdoh, Urban Dictionary, Network Dashboard, CleverToDo and Battery Meter (homebrew that runs every 10 minutes).
So, it's probably not your background tasks. I did read in the Nokia manual that Camera should not be left running in the background as it can affect battery. I have a habit of backing out of all apps often during the day. Try that before you set it down for the night. Sounds like you drain might have been related to a signal issue though.
Sent from my Lumia 900 using Board Express Pro