Soldato
If you haven't updated the phone, the battery life shouldn't just change randomly unless you've got several things syncing you didn't have before, or if its faulty.
There are reported battery issues (they dont affect everyone though, strangely) on the newer firmwares so are you sure you haven't updated it by mistake?
No, I avoided any update because my handset seemed stable and there were known issues with the later releases of firmware, plus I was thinking of jailbraking at some point. Wi-fi and 3G are turned off and I've reduced the brightness levels. Although I've connected to iTunes a couple of times in the last week I don't think anything has been altered apart from a few app updates.