...that I did not know that the rear cover of my Samsung S8+ was a plastic shell covered in an ultra thin glass layer.
If I had known this before attempting to remove it fully (it was split away from the main frame of the phone due to the swollen battery inside the phone) I might have been a little gentler and maybe (just maybe) my cow's tit$ fingers would have been gentler in their approach. A million tiny shards of glass later the back was off the phone.
The fingerprint sensor, torch lens and camera lens cover-glass window were absolute ba$tards to prize off the now crumbling glass-paper/plastic of the rear cover.
The old battery out/new battery in was not too difficult (15 screws out/in and a few Anglo-Saxon words of encouragement).
Cow's-tit-fingers notwithstanding the SIM/SD card carrier somehow got broken and jammed in its slide-carrier and had to be coaxed out of the guts of the phone.
Once superglued back together it was re-inserted and thankfully was recognised by the phone. It works! Bluetooth earbuds all working, front video camera all working, wireless charging working.
Cost of new phone (if I could not repair this one) £349...... Dodged that one.
Cost of new battery £20. .... Mixed reviews, some say its great a few say they thought the battery was crap.
Cost of new rear cover (on its way) £20. .....no idea yet, most of the reviews are positive.