Hi, error 506 batlow pebo, one of four battery not charging, battery swap helps for a few days. Have any ideas?

Try to replace the charger connectors from BAT1 to BAT2 , and from BAT2 to BAT1, and check if the other battery will make fault, also when replacing batteries need to replace them in pair (2 pcs.), if this does not help it means that the charger is faulty,
i solved same issue with adding additional stand alone battery charger directly to battery which does not charge.
Hope i helped you

Thanks, in my pebo is 4 battery, and changing not helps, but I will try connect 2 battery to one charger output.