This is the same post entered over at xda-developers link:
http://forum.xda-developers.com/showthread.php?p=10196741#post10196741
[QUOTE=skullnubien;10164788]Hi
After the latest OTA update to stock Android version 2.2.1 the phone is now draining battery like crazy. When I look at the battery log, it shows that Android System using more than 30% of battery life and increases even when the screen is turned off. I used watchdog app to check the issue, and again Android system tops the list. I have disabled auto-sync, attempted even to disable wifi and data connectivity all together, still with no luck.The phone used to last at least half a day with normal use, but now it goes nowhere near 5 hours with screen turned off!! I have reset the phone to factory defaults a couple of times now, and nothing changes. I have been with this new version for about 4 days now.Any ideas?? Possibly a downgrade option??
Thanks in advance.[/QUOTE]
Hi
I have found a solution for this issue that so far seems to work. After noticing that not even after resetting to factory defaults, Android System (process) persisted in misbehaving, I decided to take a different approach. The procedure involves resetting the phone to factory defaults but this time via the bootloader and recovery menu. To note that my device is not and has not yet been rooted so all options mentioned should be available in your ROM (I guess).
[B]Procedure:[/B]
1st – Make sure that all your data is backed up(I use Mybackup pro)
2nd – Turn fast boot off: Settings>Applications>(uncheck)Fastboot
3rd – Now turn the phone Off (Power button and select power Off)
4th – Pressing the volume down button (don’t release) then tap the Power button once and with the volume down key still pressed, a white (hBoot) screen should appear as the image shows.
5th – First using the volume up/down to navigate through the options and power button to select: you select RECOVERY#The phone should restart in Recovery mode: a picture of the phone with an exclamation mark is presented as per below image.
6th – Pressing VOLUME UP and POWER BUTTON should give you different option, scroll down and select Wipe data/factory reset. This should reset the Android side of things and wipe the Cache folder also.
7th – After that is done, you want to reboot the system back into the white (hBoot) screen, so select the first option and whilst rebooting keep the VOLUME DOWN button pressed. Once in the recovery menu you select FACTORY RESET.
At this point the phone should start up as normal and you set everything up again and it should be back to normal. I Would advise to wait a few minutes before restoring your backed up data, the apps should be fine to be restored.This method worked well for me, the device has been of the charge at around 3 am [GMT] and remains with 30% at 17:45h after restoration and with normal use after about 10am.
Hope this works for you.
Technube 
Rune Pedersen
April 7, 2012
Hi. Evereything works like the description above, but the phone is unable to reset the cache memory, or reset the factory settings – so I’m unable to restart it. It just freezes up om me… Any ideas on why?
Felin00b
April 8, 2012
Hi, just to confirm, have you tried to apply the instructions described on the post?
If so, are you using stock, operator modified or custom rom? Based only on what you’re describing, I could only advise you to pull the battery out, place it back in after a short while then try the guide I described in this post. Let me know how it goes.