Also when installing new battery, note battery does not fill up entire space so there is some discretion on positioning.  In reference to above photo, make sure new battery is shifted slightly to right (towards top of phone) so as to not lay on top of circuit board below (left in photo).  After reassembling mine the phone speaker would not work, so I took it apart again and figured out the battery connector harness was partially on top of the circuit board and interfering with needed electrical contact between the mid-frame and the circuit board.  Easily fixed by adjusting battery position.  Fortunately I had tested phone operation BEFORE reattaching back cover so this was an easy fix.