The iPhone 4S features the fastest Apple A5 Dual Core processor, a slightly more powerful battery and a camera of 8 megapixels with an 'open ƒ2.4.
The battery while it is similar (cone size as the one on iPhone 4) has a slightly higher capacity equal to 5.3 Whr, A sign that most talk time stated by Apple is to be found mainly in the optimization of hardware and software. It improves the talk time of an hour in some cases it reduces the standby time of 300 to 200 hours.
As previously mentioned the iPhone 4S features the fastest processor Apple A5 Dual Core (the same iPad 2 to speak, but with a reduced clock speed)
Here's the logic board: