Ebiumn, as the last resort before replacement of the whole device, we can try to diagnose the battery - maybe it's just the battery on the malfunctioning device that needs to be replaced, not the whole reader.
I suggest that you swap batteries between devices and see whether the sane PB works with the suspect battery from the malfunctioning PB and vice-versa - if the sick reader will get well when connected to the good battery.
Please, mark the batteries before swapping!
