Purpose of serpentine routing on battery balance circuit PCB
It is thermal decoupling of the relatively small transistor from the power resistor.  Such that they can be physically close without risking the power resistor heating up the transistor and causing it's characteristics to change.

Guessing this is a MOSFET (the top mark A2xxx is too vague to be sure) The source-drain resistance increases with temperature, leading to a rise in power dissipation and hence thermal runnaway.

Preventing the initial external heating would help prevent the possibility.