While I have seen a lot of reports of really bad battery life on the iPhone 4S with iOS5 I haven’t seen many articles about battery issues on the iPhone 4. I have had some major battery issues since my upgrade, unplugging my fully charged iPhone 4 at 8:30am not using it through the day it usually ends up at about 12% charge left at 6:30pm.
I came across an apple forum post that may or may not help, I just disabled this feature today.
I upgraded my ipone 4 to ios5 and had the same issue. I did the same thing everybody did and turned all the cool fetures off, I even went to apple. I could litterally watch the batter drop. I started looking again and found a new feature on ios 5 called diagnostics & usage under settings, general, about. If you click on it and changed to don’t send rather than automatic send your battery life will be back to normal. I looked up the reoports it was sending down where it says diagnostic & usage data, and found my phone was sending out around 200 reports a day back to apple. This is what was draining my battery and most likely yours too. Apple uses this to help diagnose problems with the ios and apps. Good Luck!
Thought I would repost it here as I had a hard time finding it in the first place.