Balance charging connection for 2 cell li-ion
The charger will need 5 connections, +ve and -ve charger outputs, and three to the balance port. I know the charger and the outer balance lines are duplicated at the battery, but they're required at the charger.

If you charge a battery that's also powering a load, the charger will misread the battery charge current, as it's not able to measure the load current. Depending on the load current, it may undercharge the battery, or report it faulty and refuse to charge it. Charge on load requires a charger that knows about the load.