Main connector is a mini Tamiya, small connector is a JST. The small one plugs into the white socket on the side of the B6, line up the black (-ve) wire with the -ve side of the socket (it's designed for also charging bigger batteries with more cells).
Note that the mini Tamiya IS NOT wired the same as the RC wiring of the same connector. If you buy adaptors make sure you get the right (airsoft) type.