How to charge and use a salvaged laptop battery with BMS?
The connector probably includes connections for SMbus or similar, and a thermistor to go to the host controller. Unless you're willing to reverse-engineer all that stuff, seems like using the pack as-is is a dead end.

That all said, if the laptop was old it is likely the batteries have reached the end of their useful life so it's probably not worth the effort when you can get fresh new cells with an integrated safety circuit as a ready-to-use assembly.