I heard the drama about iPhone batteries, I know my phone is many years old now, and I was already feeling that my phone was drastically slower than it had been when I first got it. The last straw came at the end of 2017, when had been well below 0 degrees F every day in the weeks following Christmas.
My grandparents were visiting from Europe, and I queued up GoogleMaps and got into my (very very cold) car to go pick them up at their hotel. Despite being plugged in to an external battery, my phone went from charged to 0% battery in a matter of seconds, and then refused to turn on. It would not turn on and begin to charge, despite being plugged in, until the car warmed up. This continued every day, as I tried to shuttle family members between various homes, restaurants, and other get-togethers.
I saw an article about how long the wait was for Apple to replace batteries, that suggested iFixit as an alternative, and I went for it.
Overall, pretty well. The guides were straightforward, the kit from iFixit had what I needed. I ended up needing to find a larger Phillips screwdriver than any of the ones provided for a couple of the screws, but this was something I had on hand so no big deal.
The repair went downhill when I tried to reassemble-- my screen was all lines, nothing recognizable, and touch did not appear to be working.
I followed many of the comments on the guide itself, cycling power, attempting to make the ports connect up better, etc, and ultimately determined that I had slightly bent the little metal humdingies for the LCD and touch functions. This was only barely visible without magnification.
I very carefully bent the two back to some semblance of shape with two pairs of pliers-- it was obvious that they connected better because they clicked in with a very clear sound when they were correct.
After that I had a few white lines at the top of my screen, but the rest worked perfectly. Trusting a user comment from the guide-- I waited, left the phone on, and these white lines faded over time, and now are no longer visible.
Be very careful when removing the little metal things from the ports-- the guides tell you to be careful not to pull the port itself off of the circuit board, but they are NOT clear that you need to be REALLY careful that what you do can cause the metal pieces themselves to become bent and no longer reconnect correctly. Advice on how to remove these without bending them would be very helpful.