@hummbug did you ever get your custom settings to work? I think I'm dealing with the same thing. Trying to write custom values over serial using python+minmalmodbus. I can get certain settings to stick (battery capacity/Ah, battery type), but none of the voltage settings will change. I write the values according to the rover modbus doc linked here (and using the same code as the settings that work), but when I read them back, it's just the default values. I've tried different values for battery type to see if the value for custom isn't what you'd expect (5) to no avail. Assuming at this point I'd be better off just buying a standard battery.