Battery swaps on two iPhone 5s' (time is total time for both)
Batteries both 4+ years old. Phone usability greatly reduced. Random shutdowns. "coconutBattery" macOS app for getting Mac battery stats lets you plug in an iOS device and get the same information. The batteries were down to ~50% and ~30% of their original capacities.
Phone #1: Disassembly went fine. iSlack worked great; glad I bought it. One adhesive strip under battery came out fine. The second snapped off right at the top. Had to pry battery out with an old Starbucks card. Hardest part of reassembly was the home button cable and bracket. Easier for lefties. No heating was needed to remove battery.
Spoke to friend who worked as an Apple Genius until recently and got some advice before doing second phone (see advice, below).
Phone #2: Had the issue with the glass separating from LCD when I used the iSlack. Prying advice in guide got me through. Battery adhesive strip #1, I thought I'd gotten the whole thing, but found out I'd really only gotten half. #2 snapped immediately, prying with card revealed I hadn't gotten out all of strip #1. Resorted to hair dryer to soften adhesive. Finish and reassembly went easily. Very glad I completely drained battery because on this phone the battery got a little curved from prying.
I went very slowly, and used a head-mounted magnifier with a bright white light built in. I doubt whether I could have done this repair with my old eyes even with my reading glasses, without magnification and bright lighting.
I drained both phones down to zero/shutoff to discharge as much as possible. Helped me worry less about flaming batteries when it came to necessary prying against battery adhesive.
I used little Dixie cups for parts after labeling them (bottom screws; home button bracket; especially for the red, orange, yellow, green screws, etc). Just set them back far enough that you don't knock a couple over (which I did).
Apple Genius advice: Roll the battery adhesive around a pencil as you draw it out. For the home button and bracket, you don't have to work with the screen directly over the rest of the phone; you can swivel the bottom of the screen enough to the right to free both hands and much more easily finish reinstalling home button cable and especially the bracket.
I bought the battery kit with screwdriver, spudgers, etc rather than just the batteries. Very much worth the few bucks I'd have saved just getting the battery.