It would probably be easier to just splice the wires on the battery’s side. Cut the fabric off that holds the wires together, and then, one at a time (not the whole lot at once or you’ll short the battery!), cut each wire and solder a longer wire between them.
Goal is something that has essentially the same length and width as the mainboard and keyboard, but I have a lot fewer constraints on the depth. So I want to stack the battery underneath the mainboard and the keyboard directly on top (with a custom case to get everything to stack, although I haven’t worked that part out yet completely.) I don’t need that much more length, but the real problem is that the connector is not flexible enough to wrap all the way around under the board.
Yeah I though about something like that but was not confident there was enough length of actual wire under the fabric to be able to solder my own wires onto it (and I will confess that I am particularly afraid of soldering Li-Ion batteries given their “exciting” properties when shorted.). Have you done this successfully or have heard of someone else doing it?
For now I may just use a USB-C power bank I have lying around since that works as a temporary measure. Not ideal though, so still be happy to hear success stories based on the above to give me the confidence that I can pull it off!
That should be a standard-ish 2.0mm pitch wire-to-board connector where other brands would have parts that interoperate. That isn’t something we’ve tried though.