I think I’m a relatively light user of my phone. I check email periodically during the day and talk only a few minutes a day. I usually get down to maybe 60%+ battery before I get home after work. I plug in every night out of habit so my phone is rarely at risk of running out of juice.
Recently my battery started dying really quickly. I would unplug when heading out the door to work, and before lunch my phone had shut off due to dead battery. I had rebooted the phone to make sure that it was in a clean state with no luck. Then I went through and turned off wireless, bluetooth, push notifications, and everything else I could think of. Same situation. I even tried a factory reset of my device and restored the backup.
Now I was getting desperate and considered taking it back to the Apple Store and seeing what they thought. As a last ditch effort I started removing applications. I had it back to pretty much out of the box with no extra applications on it.
The only thing that was left on there that was configured specifically was my email account using the Microsoft Exchange Active Sync connection. I didn’t think that all this would be caused by that because that should just work right? As my last resort before going to the store I deleted that account having it remove all my data, and then set it up again fresh. Sure enough, battery life restored. I loaded all my applications back and it was back to normal.