just having a soak in the bath and it suddenly came to me why when on hookup all three batteries were getting charged,will check it out tomorrow before embarrassing myself as to what the cause was
Voltage sensing split charge relays do not always work very well with mains chargers or solar panels , as the voltage increases they think the engine is running and split the charge when you maybe don't want it splitting ?....
In my experience it's better to have a alternator triggered manual relay if you have a mains charger onto one of the batterys when on hook up