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.