I have an iphone 4s. the battery life is awful. I have found a way (that works for me) to increase the battery life by at least double.
it has to do with location services.
go to settings > location services > system
turn them all off.
this will prevent the location services from being constantly on.
also, while you are there look for any apps that are using location services (that shouldnt be, like foursquare) and turn them off.
by specifically turning off location services for these apps it means that they arent allowed to use the location services, so some things might not work properly, but at least you will have power in your phone.
i think that apple should limit the location services to apps that are currently running and arent backgrounded. there is no need for foursquare (or anything else) to know where I am, unless I am specifically checking in, or looking up a map etc.
you should also disable any geofences (like location reminders in the reminders app) if you arent actually using them