My wife accidentally upgraded the iOS while syncing her iPhone with iTunes. That's fine as she doesn't need jailbreaking. However, after the upgrade, the battery drained so quickly that she needed to recharge it after half-day use. It's just normal usage - a few phone calls, couple email checks and some web browsing. The battery life even decreased quite significantly while the iPhone is just in sleep mode.
The iOS 4.3.5 is supposed to be a minor update that fixes a security loophole. There should be no enhancement and feature improvement. It really surprised me why the battery life degraded so seriously after the upgrade.
If you also experience the batter drain issue, you're not alone. As I did a search on Google, I found some users also complained about the problem on Apple's discussion forum.
So, how to resolve the battery drain issue?
It turned out there is an easy solution to rectify the problem. It's really simple. Just press both Sleep and Home button to do a hard reset. After the reset, the battery life is back to normal!
If this doesn't work for you, here is another solution that you can take a look. Try to perform a full restore of iOS 4.3.5 using iTunes. But remember to backup your iPhone's data before running the restore. This ensures you can sync back all the content and restore your iPhone to the previous state.
The original post was published here: iPhone Battery Drain Issue After iOS 4.3.5 Upgrade