The Ifixit battery comes with new adhesive strips already attached to the battery. Suggest that it’s best to leave the protective acetate over the strips until AFTER the new battery is re-connected and the connector cover is reinstalled (2 screws). Then its easy to remove the acetate cover from the adhesive strips and locate the battery.
If the battery is stuck in (with the adhesive strips BEFORE the connector is correctly installed it is impossible to adjust the position of the battery to align the connector.
I question whether Steps 12-18 (separating the display from the case) is actually necessary? The battery can be removed/replaced with the display connected (but standing upright, as displayed in Step 7.
Leaving the display attached obviates the most difficult steps (re-connecting the various control ribbons — 3/4 of ‘em!
I followed this manual completely and the repair was successful. But if I had this to do over, I’d leave the display connected.