A battery rack and a PCS look like they are joined by a single cable, but two interfaces — power and communication — must line up simultaneously before the system will come up. On the power side, changing the number of series cells in a rack shifts both ends of the DC voltage window at once, so checking one end leaves the PCS unable to start in the low-SOC region. On the communication side, the register map and scale factors sit outside what the standard defines, so a single unit mismatch makes SOC read ten times high. Every figure below is an assumed value for illustration and must be recalculated…