Unsure with fc40 but the battery itself normally charges by the white plug,,whether or not the orange plugs original I not sure unless the fc40 plug was changed at some point,looking at the charger and extra wires I think he thought it might charge mayby,I have not seen that tryed and I have changed and chopped plugs all over rc stuff,,if you haven't tryed to charge I would test with a multimeter to see what's coming out !! Like they say lipos bit on the explosive side if shorted out so I'm suspicious about that,,,hey I might be totally wrong,,see if you can find what original battery look like cause me t,rex runs similar,
Hopefully some chime in when time zone hits and you find out some more,,I'm curious too