I think the video shows not all parts, the connection to the battery is missing.
Some time ago I made a 3D CT-XRay-scan of my P90R:
It seems to me that there are wires welded (not soldered) to the battery. Soldering is a no go in this case. Welding can be done in a real short time preventing the part to heat up. .
Note: There are only metal parts visible.
I think also the goal was to achieve more reliabilty. Replaceable batteries have disadvantages, contacts may corrode, sealing of the battery door etc.
Probably the rechargeable batteries Phonak uses are custom made. Therefore it will not be possible to buy them anywhere.
EDIT:
It might be possible to solder the wires on the PCB. If we get the replacement-battery with the wires attached.
