I have both the 720 and the 615 and usually don't use the balancer for 1s since it's not really needed, though the display always says balancer not connected. If you are going to try the balancer port, you will need to modify the adapter to put the small pin (middle on a 2s) to plug into the battery and the positive or negative disconnected. Using it as shown, the voltage of the 1s will show up on the 2nd cell in the balancer which is likely not being looked at.