Thanks so much for the comments.
After viewing in-stock battery clips, did get the impression it was custom.
Interesting suggestions re: part from a broken one, foil /paperclip, and shape-your-own (not set up to re-plate).
Since it’s summer here, do have a while to explore options before the next heating season.
PS For future reference, does this sort of exposed PCB trace (pad?) used for electrical connection take solder well?
Thanks for the self-help suggestion, and the product link (my search-terms must indeed have been inadequate)…