If you are observing poor battery life after unlocking your iPhone using a combination of PwnageTool or Redsn0w to update baseband to 06.15.00 and Ultrasn0w 1.2 for iOS 4.2.1 then you are not alone as some readers have reported the issue.
According to iPhone hacking expert, Sherif Hasim, it looks like the reason for the poor battery life issue is the hacktivation process used in PwnageTool and Redsn0w and not Ultrasn0w 1.2.
Sherif Hasim explains:
On a very important side note, before anyone starts to complain about battery drainage issues after installing the new ultrasn0w on the 6.15.00 updated BB, the culprit here is not ultrasn0w, it’s the hacktivation process (activating the phone by pwnage tool or redsn0w rather than using an official carrier sim to do so) that u mostly did while jailbreaking.
The 4.1 and 4.2.1 ipsws unlike their old ancestors, seem to keep looking for valid push certificates all the time, either thru your wifi, or thru your cellular data network (which u only have after installing ultrasn0w and hence u accuse it) , this can be seen clearly if u have a cellular working data plan for 3g or edge and u watched the settings > general > usage > cellular network data (sent & received are continuously increasing even without using any internet traffics on the phone) , this will also render the phone going hot even in stand by mode and also very rapid battery drainage occurs plus consuming ur data if you were not on an unlimited plan.
The good news is that, one of the iPhone Dev team members is working hard to fix the issue. Meanwhile, you can also try to fix this issue by borrowing the SIM of an official iPhone carrier from your friend and using it to activate your iPhone via iTunes.
Have you observed poor battery life after unlocking your iPhone? Tell us in the comments section below.