The camera in my 6 Plus had gone bad a months ago and was getting worse. The image stabilizer would jerk the camera off center on its own every second or so. Apple store said it may be the camera, but it could also be the motherboard. :/ I decided to just change the camera myself with parts from iFixit. I decided I'd replace the battery and lower speaker too while I was in there since the parts are so affordable from here.
Following the battery replacement video, I was able to access the other parts as well, and had it all done in about an hour or two. So great to have my camera working great again and taking vids and awesome pics! The speaker is crystal clear again and my battery lasts way longer than I remember it everlasting before. But maybe it did last this long two years ago? I also replaced the battery on my brother's iPhone 6. His battery had been wonkey for a while. It would jump from 100% to like 20% spontaneously. He had to use a battery backup case just to make his phone useable. But it's back to good now !
When applying the sticky strips to the back of the batteries, I peeled off the wrong side of the plastic first, and ruined them. I tried to use them anyway, all bunched up at one end. But it made my battery sit a little higher because the strips weren't laying flat. The raised battery was actually pushing again the back of my screen and causing discolored spots. I had to order another set of sticky strips. I replaced them yesterday and everything is all good now. Be sure to watch the applying adhesive strips video on youtube at youtube.com/ifixityourself.