Panasonic FZ-G1 3 pinout maybe

| PIN |         | Description         |
|-----+---------+---------------------+
|  01 | Shield  |                     |
|  02 |         |                     |
|  03 |         |                     |
|  04 | GRND    |                     |
|  05 | 16V     | Supply (for dock ?) |
|  06 | 16V     |                     |
|  07 | 16V     |                     |
|  08 | 5V      | Supply for usb ?    |
|  09 | 5V      |                     |
|  10 | 5V      |                     |
|  11 | GRND    |                     |
|  12 | D-      | USB D-              |
|  13 | D+      | USB D+              |
|  14 | GRND    |                     |
|  15 | TX+     | ETHERNET TX+        |
|  16 | TX-     | ETHERNET TX-        |
|  17 | GRND    |                     |
|  18 | RX +    | ETHERNET RX+        |
|  19 | RX-     | ETHERNET RX-        |
|  20 | GRND    |                     |
|  21 |         |                     |
|  22 | SHORT ? |                     |
|  23 |         |                     |
|  24 |         |                     |

As you can see

Just for reference
I happen to have one of theese: https://www.bobjohnson.com/gamber-johnson-tabcruzer-dock-for-panasonic-toughpad-fz-g1/

I once opened it and tried to take some pictures for figuring out the pinout.

Some notes I made while comparing the TabCruzer to the iKey-keyboard

@datorvictor thanks for all the info, I would like to make a cheap dock or at least a connector
Dont know about those other connectors but yes I do not think they use USB for that

If the BatteryBridge is a 7,2v 350mAh two-cell Li-ion meant to keep the computer running while you replace the main battery., could you use two 3,6v 3000mAh 18620 cells, or similar as a secondary battery for the system?
Or if there are i2c-busses/similar, you could add RGB-ledlights, compasses whatnot....
I am using my unit as a dedicated spectrum display with a LimeSDR usb3 -radio and I have toyed with the idea to some how mount the radio to the computer case. So theese findings are quite nice in that regard. for.ex. the bridgeBattey cover could be replaced with a case for the LimeSDR with usb3 routed from the bottom expansion connector.

Something like this might work. the connectors pitch is 1.5mm and pogopings from aliexpress:

https://www.aliexpress.com/item/33044114576.html?

That looks great, I would add two holes for mounting to the body of the mechanical design, or to use the two holes of the plastic piece in the tablet

I have been thinking about it. The lowest profile pogo-pins I found with little effort was 2mm tall with a 1mm moving tip. so there would still be a 2mm gap between the PCB and the expansion-connector. So in my mind it will need some kind of thicker 3d-printed exclosure, propably with holes for pogopins and a and neccessary holes and tabs for fixing the whole thing over the expansion-connector.

of course this can be modified, for example the profile could be lower/thinner if the pogo-pins were replaced with something different.
I have tried to find single springloaded compression contact used in some battery terminals. picture bellow. But they all seem to be pre-packed with standard pithches, not fitting over the expansion-connector.

and two details about my design, I tend to do my prototyping on a single-sided PCB, etched at home.

1. precise alignment, that’s why the chosen pogopins are through hole components with a tab
2. rest of the components are on the opposite side of the PCB so it can lie as flat as possible.

And now that I complained about the spring-loaded connectors, aliexpress offered them directly… :D
https://www.aliexpress.com/item/1005005574169122.html?

The B22A0 spring loaded connector seem to be a good choice, don't know how to solder those connectors tough
Would be awesome to find a 1,5mm pitch connector but I think those single connectors are the way to go