Please be aware that your battery-pack contains a large amount of energy, which can be potentially dangerous. Use isolated spanners, to prevent any short circuits.
High inrush currents, causing arcing (sparks) and ultra-high electromagnetic levels, can easily damage electronic circuits.
We therefore strongly recommend to always connect the "terminal connections" FIRST, and THEN connect the BMS-boards separately.
The recommended technique of doing this is shown in the photos.