[SOLVED] (for me anyways)
BATTERY DRAIN ON ICS
I also experienced a dramatic loss in battery life after the ICS update. After reading much online about others experiences and after doing some testing of my own I finally have my battery life back to normal... even better than before when I was on Gingerbread. However, it is somewhat of a pain to manage. I discovered 4 things affecting my battery life... WiFi, 4G Wimax, and 2 apps (Juice Defender and InstaMapper GPS Tracker). I installed CPU Spy and BetterBatteryStats to moniter what was happening to my phone. In a nutshell WiFi and 4G Wimax keep the phone from going into deep sleep. So I disable WiFi and 4G and enable 3G when not using the phone. (Menu... Settings... toggle both WiFi & 4G off. Menu... Settings... More... Mobile Networks... check 3G Data) That would have been enough except for the 2 rogue apps I mention above. Juice Defender and InstaMapper GPS Tracker seem to enable WiFi and 4G even when I manually disable these. So I uninstalled these apps. (There may be other apps that you are using that also disregard your manual settings and enable WiFi and 4G.) When not on WiFi nor 4G and only using 3G, the phone does go into deep sleep and stay there until I wake it. So you can see it is manageable, but a pain or at least slight inconvenience. With moderate usage, including turning on/off my WiFi and 4G throughout the day, I have 20+ hours of usable battery life. I hope this helps.
I'd like to know if this works for anyone else. Also, I was thinking that both Juice Defender and InstaMapper GPS Tracker have setting that regulate their access to the antennas and it may be possible to tweak the settings to bring battery life into acceptable range. Didn't think much about it, because I don't really need these apps. Anyways, the above solution works for me. I did NOT do a factory reset and don't really want to; however, it is possible that a factory reset may/might resolve the battery drain problem.
I agree that Juice Defender was also a culprit of the battery going bezerk because after I initially got my ICS update, I used Juice Defender and it was making my phone go crazy! After I performed a factory reset, set wifi off (unless I need to use it but immediately shut it off right after usage), have mobile network set to 3G, using another home launcher (Holo Launcher), a few little odds and ends...so far, my battery today has been excellent. I woke up this morning around 7:00am with a full charge..now, I am looking at my phone and it still has 51% juice left on it. This is with moderate usage (text messges, emails, phone calls, few FB views w/wifi, etc.). I also make it a habit of clearing the cache often along with clearing out those running apps in the background before I exit from my phone (long-press home button and swipe running tasks to remove from background). I have to give credit to the whole community because everyone has been posting all of their suggestions, opinions, rants, and raves that I have been reading. Even though this has been somewhat of an unusual software upgrade experience but nothing that has not caused pain, suffering, or loss of time/work from my life.