My iPhone battery was in need of replacement. I wondered if I could do it especially in the light of some stories of the problems people had had attempting the same but $70 saved was worth the trouble.
I took my time and read as much as I could.
The screen came off quicker than I expected and one ribbon was disconnected immediately but wasn't damaged. Do open it from the button end and only open it to 45 degrees so the ribbon doesn't pop out by itself.
I was very patient getting the battery unstuck and began to hear a satisfying sound of the sticky coming unstuck so didn't rush and it was fine.
Putting things back in was a bit fiddly but patience paid off.
Make sure you don't bury cables behind the battery and jiggle carefully the logic board as you take it out and put it in to make sure you see the grounding tab and don't break or bend it at step 14
I found the instructions about the white/black tab on connector 3 being flicked up to release the ribbon confusing. However it is exactly at it says: use your spludger to nudge the tiny tab on the connector that is opposite where the ribbon goes into the connector and it will flick up from a horizontal position to a vertical position and the ribbon will slip in and out easily.
I carefully placed screws in order as I took them out so they went back exactly where they came from.
In the end it took me an hour because I keep double checking when I was hesitant. The battery already had some charge and it all worked fine.
Take you time and review instructions at each step.
Make sure the ribbons are well seated in their places and it is awkward at points with little connectors and big fingers but a step at a time and you'll be fine.
Did I mention take your time?