Very weak battery
Very straightforward except the suction cup wasn't strong enough to open the screen. It took me more than 30 tries before I got the prying tool inserted between the screen and the case. I almost gave up.
Pull up on the screen with the suction cup while using the blue prying tool to push down on the case. No need to unplug and completely remove the screen. It helped to heat the back of the phone to loosen the battery adhesive tape.