The degration in battery life could be due to an
app, if you’ve identified the app that may be hogging your iPhone’s
battery life then force it to close. Hold down the Sleep/Wake button for
a few seconds until a red slider appears, then hold down the Home
button  until the app closes. You can also remove an app from the app
switcher to force it to close.
The Next Web is reporting that some iPhone users are reporting issues with battery life and overheating after upgrading to iOS 6.1.
Strangely we’ve heard contradictory reports from our readers. Some of them have told us in this post that they’re actually seeing improved battery life, while some have reported that iOS 6.1 has made things worse.
Steps which can Make your phone last longer >>>
Force an app to close:
Turn off/Turn on Location Services:
Turn off location services for the apps (Settings -> Privacy -> Location Services) and then turn them back on one by one to identify which one is causing the drain on battery life.
It is also a good idea to review the list of apps that are using Location services, and disable it for apps you think can be used without tracking your location.
Restart/Reset Your iPhone:
Hold down the Sleep/Wake button and the Home button at the same time for at least ten seconds, until the Apple logo appears.
Resetting Network Settings:
Reset network settings by tapping Settings -> General -> Reset -> Reset Network Settings. This will reset all network settings, including passwords, VPN, and APN settings.