Galvanic Isolator/ Battery Charger

My power usage is pretty minimal as I use only one light at a time, and the rear of my boat doesn't have any lights at all. I do have a waterpump though. However, I still need to charge my batteries and the need for this will increase as I sort out my bathroom and install a shower pump. I have been looking around, and after a visit to Uxbridge Boat Centre, I have decided a sterling 12v 30Amp charger is the one for me. The crucial question is whether I will need a galvanic isolator as well? I have done some searches, and see that it would be necessary as I will be using shorepower to run the charger, but is a galvanic isolator the solution? It seems all to obviously so, and there must be other solutions!?