The correct replacement battery is a Cameron Sino, model #CS-GMD560SL (p/n 361-00051-02). I bought it from NewPower99.com
The ribbon connector is held in place by a white plastic bar that snaps in place. It will pop up when lightly pried from the ribbon side as shown in the photo (the pivot action is on the connector side). Putting it back together is tricky. The ribbon cable has to lie flat in the connector as far back as possible; once this is true then snap the lever flat against the cable and lock it in place. You might feel a very subtle snap sensation.
The battery is glued down, so use of monofilament fishing line (with each end tied to metal washers for handling) in a zig-zag motion underneath will help break the adhesive’s bond.
Yet another G4 QuickSilver saved from the electronics recycler! In tandem with an eBay-listed refurbisher of my defunct PSU, it was brought back to life. Instructions were very clear.
This step can be done prior to Step 13.
This step is skipped during disassembly.