Dev-Team released PwnageTool and Redsn0w to jailbreak iOS 4.2.1 and update iPhone 3GS/3G baseband to 06.15.00 which is unlockable with UltraSn0w 1.2. However, many users are reporting poor battery performance after the jailbreak/unlock.
According to Sherrif Hashim:
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 pwnagetool 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.
How to Fix Battery Drain After iPhone 3GS/3G Baseband 06.15.00 Unlock
While an official fix for battery drain issue is currently being worked on OUT Now (See C below), you can try the solutions listed below to fix the battery drain problem.
A) try to activate the phone using the official sim if u have it (even if the sim itself is old and not working) , or borrow it from a friend if it’s possible, by any means, try to have an access to one and use it.
B) if A is not feasible, u can install SBsettings from featured cydia packages and turn wifi and data off when u r not using it (shuts down both 3g and edge) , till C is done
C) there is a very nice module being worked on by a trusted jailbreak app dev, namely @sbingner, which will resolve that issue for those having it, the details of which shouldn’t be disclosed until he finishes his awesome work, till then, either use A or B to resolve the issue if it exists for you. Solution is out now: