I've never changed the battery in my IPhone but my MBPr 15 it took an OEM battery fine. I cut the glue with some spectra fishing line and wasn't that hard. Took me about 15 minutes to replace it. The IFixit OEM battery came with the tools to change out the battery.
Older iPhones are much the same; I've done several battery and screen replacements on my 1st gen SEs. A heat gun comes in handy, but beyond a couple cheap screwdrivers most of what you need is just decent eyesight and steady hands. (I only have one of those, but can still fake the other for a few years yet before I need one of those magnifier visors.)
Newer ones, I don't know. It does look like Apple is starting to move in truth toward the hostility to DIY repair they've always been claimed, in the past often falsely, to display.
It's a shame. I really like the idea of that purple 12 mini - it'd go so well with my fountain pen! But if I can't fix it myself when it needs fixing, that's a much knottier problem.
