522760-4 switched battery voltage out of range low.
has anyone added any devices to this truck that were not factory, like a scale, camera, b/u alarm or impact alarm?
this can be a bad relay or the relay box [Hyster calls it the power distribution box] itself, but in my experience, it is far more likely to be related to added items that were not properly wired into the system using the proper power supply taps supplied by the system.
since the error and failure is in reverse, I would first remove the backup alarm wiring.