http://www.cnn.com/2012/05/04/tech/mobile/iphone-bigger-screen/index.html

This article is about how the Iphone 5 will have a 4" screen instead of a 3.5" screen. They say that the smaller size battery dies faster, but with the 4" screen they have more room for a larger battery, they have the Iphone has small as they can get it for how much stuff is inside.