My gf's iPhone 3gs for some reason never fully goes into standby, as in when it's in standby it still thinks it's being used. This causes her phone's battery percentage to drop 40% over night. It is a recurring event, and I have tried restoring from a back up, and the problem went away for awhile but it is back again. Here's pictures of what I mean. Before Bed After Bed As you can tell battery dropped 40% and when the iPhone wasn't in use it still thinks it was.