Update: I did a continuity check between pin 14 and the postive terminal of the battery holder (with the cell out) and found there is no continuity.
I don't know how, since it's a PCB trace, but I must have broken the continuity. I can't see any physical damage though.
Update: I soldered a wire between pin 14 and positive battery terminal. Battery backup works again!
Thanks everyone, especially @ShermanP for the assistance.