Possible solution for 3G battery issue (iOS4)
For 3G phones upgraded to iOS4 and having bad battery life:
My battery life took a huge dive with the upgrade.
I don't think this solution has been posted here but I was reading the Apple forums and someone there identified that crashed apps on the 3G keep processing (using data) in the background even when the phone is on stand-by or otherwise being unused. Even with the app not "open."
And if you are like me, after upgrading, you have had a handful of apps that crashed when you have tried to open them.
Most notably, the Apple Store App!
(The fix for that, and most of the crashed apps, by the way, is to delete the app, reinstall from the App Store as if new - my 4 or 5 apps that wouldn't open all opened perfectly after that)
Anyhow, the fix is -- put on your Windows hat! -- reboot the phone.
I've been streaming music for 30 minutes since I did this, and my battery bar hasn't moved! Before this, it would lose nearly half a full charge with 30 minutes of streaming.
So, if you have had an app crash - or if you have one going forward - try rebooting and see if that fixes the battery drain
(and reinstall that app!)