Only had this new (to me ) boat 6months or so so still finding my way around it all.
Currently when unplugged from shorepower my batteries (2 in the domestic bank) only last for around 4 hours with just the fridge on, radio and a couple of internal lights (standard 12V halogen downlighters) on. I've had the batteries checked and the bloke says the batteries hold their charge OK
I have a generator fitted to the boat from new which charges the batteries and I wondered if the domestic battery bank was deliberatly a smaller size due to having a generator fitted.