Hi @ThomasWR,
That connector is generally used for balancing while charging the battery, but if you’ve got suitable hardware (e.g. a microcontroller with a set of ADCs) and you’re willing to program it then those wires could also be used for measuring the voltage of each cell during operation if you wanted to.
We normally use our Power Sense Module to get continual measurements of the total battery voltage and current usage, which get communicated to the flight controller. Generally that’s sufficient, but if you’re wanting to be extra careful about battery health or something then you could set up your own system to measure each cell with the balance connector 