Why not order the "real battery" from Varta.
It is not that pricey, and is the actual battery.
When I replaced my A4k battery, I soldered 2 long leads to the motherboard. Using a plastic spray can "cap", I hot glued the cap to an area away from the motherboard. After attaching the battery to the wires, the battery was placed into the cap.
The battery was then hot glued to the bottom of the cap. Hot glue was used to also tab the wiring at the rim of the cap, and at several points along its travel back to the motherboard.
