I had my last iPhone 4 replaced, due to a seemingly bad battery and a failing home button. My new device came with iOS 4.2.1, which was a reliable version in a lot of ways, but I missed specific features of 4.3.1 itself. So after restoring the phone as new with the recent update, I went ahead and ran the battery down and charged all the way to 100% to recalibrate. After about a day, here are my results: I unplugged the iPhone at around 5am yesterday, and it is now hovering at 50% at 12am. Personally, I think the battery is fine. What say you???