The battery on my 3+ year-old iPhone 3g had bit the farm. Even after a full evening of charging, it would shutdown after only 10 minutes of e-mail or other use. I resorted to using an external battery case for several months, which pretty much negates the svelte appeal of the iPhone.
Swimmingly. Though, I did wait until my new iPhone 4s arrived and was fully running. Must say, small and steady hands are quite crucial to this kind of work. Not my hands at all. The toughest part was removing the display; I nearly gave up after 10 futile and anxious minutes of struggle. But then I cottoned on that it required a "prying" action, so I levered the pressure applied by the suction cup. Some wiggling and levering finally loosened the display, and then it was easy peasy. The second toughest part was removing the old battery because of the adhesive. It should be noted that there is nothing (apparently) of critical importance beneath the battery, so more force can be applied without fear of damage. That would be good to note. The third difficult bit was removing ribbon #2, but only because the direction is unclear. There is a very narrow black tab at front of white plastic holder; once the black tab is lifted the ribbon slips out the back of the white holder. The instructions imply it's the entire white holder unit that must be lifted. That was frustrating.
Those three things aside, it was easy-ish. Terrifying because of the limited space inside, the tiny screws and the $500 device that could potentially have been destroyed had I screwed up. But done. And now that I've accomplished that, I figure I can manage about anything with the iPhone!
See details in the repair section.
And photos? Are you kidding? I could not have held a camera steady during any part of the repair.