I'd like to investigate and get your comments about the battery life issues introduced with iOS 5, which iOS 6 failed to fix, only making it worse with even more services that potentially cause problems.
It seems this doesn't affect everybody and always. For instance, Apple engineers using AT&T in cupertino do not seem very concerned by the issue, but if you are on Orange, Switzerland, it's another story. From my understanding, big battery drops (~10% / hour) are related to the way iOS handles bad cellular network conditions. Often, the iPhone will "think" it has cellular data available (o/E/3G icons next to the operator) where it actually won't be able to reach the operator and never receive a response. In this case, iOS will leave the 3G chip powered for several minutes until a timeout occurs, even having the phone locked. If mail is fetched every 30 minutes like me, it makes 5 minutes of usage per 30 minutes, and should easily drain your battery in one day.
(Note that this will also happen every time you use the calendar for example, if it's synchronized with iCloud.)
So first problem: a timeout way too long. It's an usual, but still annoying thing with OS X. Second thing, as long as iOS doesn't realize that the push connection is invalid (i.e. it thinks it has network but will actually not be able to receive anything) it's ok. If a small drop or change in connectivity happens though, the connection will be reinited, and that's where things get very bad. The connection may fail at that point: 5 minutes of battery usage (~2% battery), but iOS will try to reopen it right afterwards. If connectivity is not properly restored, 5 more minutes lost, and so on. This is shown as usage when you go to Settings > General > Usage.
Yes, my mother did not use her iPhone 4S a single time after charging it yesterday, yet it was dead at the end of the day with 3 hours 30 minutes of usage. This do not happen on Android devices like my father's Galaxy S, who uses the same operator.
For people who have battery life issues, have you observed something like this on your iPhone too?