Based on the pins in your other picture, clk and data are probably an I2C interface, int is for sending hardware interrupts, not sure about "det". If you have access to an arduino or something, you might be able to try reading the output from a working BMS and then reverse engineering it for your own battery, but that's a bit of time and effort compared to a OEM part. Maybe some sort of insulator inserted to block the heat from the fan instead?

Looks really clean; the heat management in particular is pretty clever. How well does the joint hold up under use? I've only seen braze joints in fixed piping systems, just curious about the strength for other applications.