Original Battery was failing,
Bad news and good news. The procedure was straight-forward in the guide. I used the option to NOT disconnect any ribbon cable connectors except the battery connector, and use the option to restrain the front section at 90-degrees with a rubber band against a heavy object. I was happily surprised to find how easy old battery removal turned out. I used a small medical pad (designed for hot or cold pack on wounds), heated in microwave to warm iPhone back before pulling old battery adhesive strips out - worked perfectly. New battery install was easy. HOWEVER, when completed, the new battery would not charge. After taking apart phone and re-attaching battery connector multiple times, I FINALLY noted a tiny single pin connector just below the battery connector was not connected. After multiple attempts with plastic tools, i managed to reattach that connector, reassembled phone and everything works perfectly.
Suggest modifying this guide to remove the vibrator (2 screws) to give better angle for pulling out old battery adhesive strips. Also, perhaps a 'warning' about that tiny single pin connector (with its tiny rubber insulator 'hat") located just below battery connector. I apparently knocked it loose when popping battery connector off.