Sir Baracas . . .
Correct me on any mark up errors.
You can see that bottom photo is telling you that the battery voltage is making it all the way across the board to those TP1 anf TP3 test points.
You stopped short of telling us if the neg or positive then made it down to the black connector.
I'm suspecting that the + makes the trip to the connector, and that you are loosing the negative path.
. . . . normal Li Ion design protocol is to monitor and switch the negative output power buss.
I believe that it will be found that the negative power flow will pass thru two series POWER FET's with VERY - VERY low RDS-on characteristics when turned on. The negative buss flow, also then goes thru a very low resistance current shunt before finally reaching the negative output connector.
Operation is this way . . . . .
That S122 should be your battery management IC to ascertain the state of charge on the individual battery cells. If low it charges, and when all is up to charged state it will activate the two series POWER FET's to give a completed power path from charger negative output to that black connectors 1 terminal.
Then the camera should then have power to work . . . . UNTIL . . . .the monitoring of the Li Ion cells , detects a progressed discharge of then having less than 2.5V from a cell.
Then it will drop FET gate bias and then a FET stops conduction and your camera is deprived of power and dead until you recharge the battery, or sometimes a rest in a warm area . . . . .z z z z z z z . . . . will give enough bounce back for just a wee bit more use time, later on.
Another aspect of the FET switching is the mentioned series shunt resistors taking the proportional voltage that is developed by the amount of power being pulled and feeding info back to the battery management IC. If it detects excess current pull, it also can open up that negative buss with a dropping of FET.
gate drive.This last application, is actually more in line with a power tool . . .drill . . .saw . . ., when it is being grossly loaded down.
I think that ? WG8G4 ? is being a dual POWER FET and your DEAD short was too much for it to handle and it is now vaporized of its die inside.
I am also wanting to think that for its power handling ability, that it is having a metal heat sinking plate on its un viewable side and depends on being soldered to a foil plane for additional lateral heat dispersion / dissipation.
Pulling one off, reads synonymous with the need / use of a hot air heat wand.
They do make 2 cell aftermarket boards like this . . . . . but . . .BOY . . . the mechanical fitting aspect !
Confirm if it is being your negative power feed thru that is being lost to the black connector.
RE- REFERENCES WITH MARKUPS
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73's de Edd . . . . .
What kind of cruel, demented person was it who put an "s" in the spelling of lisp ? Since its gonna come out as a difficult Lith-p .