I had a PCB made for me for connecting the 18650 cell holders to my Balancer/Discharger and Hobby Charger. It connects the 4 cells in series (4S).
Fred at FAR Circuits made the board:
It's explained in this link.
Here in this link is the details on how to connect the Balancer/Discharger to the holder:
You can also use the PCB and the cell holder to connect a Hobby Charger for Balance Charging.
Bill