Maybe the remaining connections are for future use, such as 3S, just a guess. Maybe it is for a thermal probe or communication, again, just a guess. I do not have the JB or LiPo, so hard to know.
From the pictures on Khadas Shop, battery is using six conductors.
The schematic shows internally, pins1-3 are tied together to VBAT, pins 4-8 tied together to ground. Pins 7 and 8 look to be something other than cell connections, again maybe for thermal probe/comm in some examples.
Not sure how this would work to balance cells, maybe JB does not operate in balance mode. From the schematic, looks like JB treats a pack as a single 7.4v cell.
All speculation for me at this point.
Look forward to your findings.