Right now there are probably many users who have a carrier unlocked iPhone running Ultrasn0w on the 6.15.00 baseband (If you're looking for a how to unlock guide, we have one here). iPhone hacker Sherif Hashim has weighed in on the problem and let users know a few things.
It's been noted that the main issue is not redsn0w, it's the hacktivation process, which is activating the phone with pwnage tool or redsn0w instead of using an official carrier SIM.
Furthermore, iPhone 4.2 and iPhone 4.2.1 are not like the older iOS builds. It turns out that they keep looking for valid push certificates constantly, through wifi and through the network. Looking at your usage data will show you this. It's noted that not only does this make the phone warm while not even in use, it can eat up battery life and use up much of your data.
Hashim has pointed out a few solutions:
1) Activate the phone using the official carrier SIM if you have it. They say even if the SIM itself is old and not working.
2) For now, if you do not have the SIM, it's suggested to try installing SBsettings from "Featured" Cydia packages and turn wifi and data off when not in use. This does note, however, that it shuts down 3G and Edge.
3) They also say that a "trusted jailbreak app dev," @sbingner, is working on a solution. Unfortunately, there is no timeframe for when it will be finished, and the only thing to do right now is one of the above two solutions until something gets fixed.
A few more notes: Some users have said that disabling push notifications helped, while others said it did nothing. Then there was a user who said that disabling push did nothing, but turning off location services fixed it entirely.
Let's hope that @sbingner finishes up soon, but for now this all you can do.
Others who are experiencing battery issues may want to check out some of our past guides: