Forcing an undercharged battery to charge?

It's actually not even turning on when not on the charger. In that thread, it seems like the battery is charging and working normally.

if its not turning on when not on the charger that would indicate the batter circuit doesn't know the battery is there to draw power.

id say if you haven't already:

check connections be sure to look for lifted contacts or bent pins.

look for corrosion on the board, typically around the chips and resistors.

make sure there aren't and SMD components that have been knocked loose \ off the board.

the SMDs can be VERY easy to brush over and pop one lose

@logixal I check with the multimeter and it is 2.9v, it's probably not enough to even show the low power screen