Jason,
If you buy the connectors without wires already mated it is pretty easy. If you use connectors from the KOP, using a small screwdriver you can release the contact from the shell. (Look in the contact end and you will see a steel spring holding the tip of the contact. Just move it out of the way and the contact will release out the wire end of the connector.) Cut off the #6 wire at the point it exits the contact. Using a large soldering iron just tin the connector and tack on the #16 from the charger. Be sure to replace the contact in the right side and check the polarity of the wiring before you use it to charge a battery. Or if you find it easier to open the crimp and release the #6 you can do that as well.