GII and GIII INS and emergency light batteries have a notorious corrosion problem when it comes to the rack plugs. It's almost guarantied that within a five ear period, they will require replacement.
The pins seem to weather the the storm quite well, but the plug housing itself deteriorates to the point that the small screws holding it to the rack can sometimes just break off.
Removal of the pins is accomplished with the white end of a yellow/white plastic tool.
The plug below was beyond repair. The removal tool would not seat down to even come close to unlocking the tabs (which were probably gone anyway).
Luckily, a unused rack plug was available for replacement.
Plug Part Number: DPXB-MA8-33S-0001
Pin Part Number: 031-1059-001