I've had an Icon for a month or more and updated to 8.1 a while ago, with a hard reset and did not restore from backup. I just got a different Icon. I did a full update while it was on 8.0, without restoring backup, including the newest firmware. I then updated to 8.1, did a hard reset, and restored from my 8.1 backup. Today is my first full day and I am amazed at the difference in battery life. At this point in the day, my other Icon would be around 40-50%. My new one, on a new battery, is at 62% and says 22 hours left. The only difference are, the latest 8.0 firmware (1417.0047), AND, I have left all the "power saving" settings at default, except I switched off battery saver. I have not changed any background apps and quite a few are allowed. I also left my 4 email accounts as default (based on my usage), except for my Exchange account, set to As Items Arrive. Otherwise, location, wifi, Ads, NFC are all on by default.
So what does this all mean? Don't really know, but I have read some things by others that if you just leave the settings as default, the battery life is pretty good.