Should I expect battery life on an iPhone 4S to be significantly worse than on a 3GS? I just upgraded from a 3GS to a 4s and my battery life is dramatically worse. I wasn't expecting it to be the same (though I was hoping that it might even be better), but I'm seeing a big difference. Since I have the same settings as I did previously, I don't think the problem has to do with any configuration differences (for example, I have email set to check manually on both). I was even running on iOS 5 on the 3GS, so I can't really point to that either. Siri is one software bit which is 4s only, but I can't imagine that is the culprit as I don't think it would always be running.

I've restarted the phone to make sure that no out of control process is running in the background.

So is the iPhone 4s just that much worse for battery life or do I have questionable hardware? Is there any easy way to troubleshoot (can Xcode be used to measure usage)?
It's anecdotal, but John Gruber (of Daring Fireball) who tends to get a lot of feedback from Apple users, suggested on Twitter that it's a problem for some non-zero percentage of users:


  
    And my iPhone 4S's battery lasts HALF a day, where the 4's battery lasted 1,5 days
  
  
  @JMoVS I know you're not alone, that other 4S users are seeing short battery life, but that's not normal. Mine lasts as long or longer.


So it sounds like you may have got a dud. If your battery life is substantially worse than a 3GS, it may be worthwhile asking to have your unit swapped for a fresh one.