[Android Q&A, Help & Troubleshooting] mr72:
When you ran the battery calibration, did you allow it to go to 4200mV before hitting the "Calibration" button? The point here is that there is a battery stats file that is used by the OS to determine when the battery is at whatever level. It will trickle charge when it thinks it's at 100%, so you may not be charging it all the way if it thinks 100% is 3700mV or something like that.

I suggest you restore the defaults and uninstall SetCPU or whatever you are using to underclock, let the OS manage the CPU (and FWIW, I am a firm believer in clocking changes to improve responsiveness and battery, but in this case ICS will do a perfectly fine job until we can OC the phone). Redo the battery calibration, it may have been reset. Your battery stats look fine, except whatever "System Tuner" is, I would uninstall that. And I don't know what "Android Core Apps" are either, they don't show up on my phone, but it is possible by debloating that I removed this stuff from my phone.

Now, this shows what is consuming your battery, but it doesn't indicate why it is going so fast. I suggest one of four things is happening:

1. Your battery stats are hosed and you need to redo the calibration

2. Whatever you did to change the CPU speed has screwed up the scheduling and you are running the phone too hot all the time

3. You normally are in a very poor cell coverage area and it spends a lot of time searching for a signal or switching towers

4. You have a defective battery

FWIW, before the ICS upgrade, I used SetCPU to set the minimum frequency to 320MHz and set it to run max of like 400MHz with the screen off, which saved a little bit of battery. But I was still getting at least 12-14 hours of solid use out of the phone on each charge, and more like 16 hours most of the time. Once upgrading to ICS my battery life has improved substantially, but frankly I think it's mostly due to two things: 1. I am using WiFi more and I think it takes less power than the 3g/4g radio and 2. wifi at my house doesn't work so the phone is basically in "No Data" mode while I am at home, and that obviously is very good for the battery. But anyway, where I used to plug in the phone on GB at the end of the day with 20% remaining, I now have usually over 40% remaining.

There are a myriad of other things you may have done or set differently that could affect battery life but I kind of doubt it is worth looking at now. And I don't believe there is any legitimate problem with upgrading without some magic image. My gut response to all of this is that in some cases the battery stats file gets munched when you upgrade and it so happens that for the small number of people that used the davemper image, it didn't get munched, but that's just the law of averages. I think it's more likely that one in 100 times or so it gets munched and you just get lucky or not. And also in my experience with working on my NC to get truly extreme battery life out of it, I found that the battery stats is rather fragile. Sometimes I will plug it into a charger and instantly it goes to 100%. I have had to run battery calibration a dozen times or more in the past year on my NC. So it's not a one-time, set-and-forget kind of thing. You have to be on top of the battery stats file especially if you are hacking on your phone.