How to calculate the size of fuse for a small battery bank
I'm increasing my RV's available 12v power from a 75ah lead acid battery on the tongue to a 412ah battery bank under the bed. All the schematics I see online show an inline fuse on the positive cable between the batteries and the charger but I'm unsure if I need one and if I do what size I'll need.
I'll have 8' of 4awg neg/pos cabling between the charger/converter and the battery box, a Victron smart shunt on the negative cable, and the battery box will contain two 206ah LiFEPO4 batteries connected in parallel. There is not a power inverter anywhere in the system - this is only designed to operate the 12v items in the RV and not any of the 115vac items. Such as the refrigerator, water pump, awning, slide, lighting, and possibly an occasional cycling of the furnace. But not the TV, microwave, A/C, or any wall outlets.
How do I determine what size fuse to install? I know the power center has a fuse for the charging system, but I don't know if that is sufficient or if I should incorporate a separate fuse inside the new battery box. Oh, and I matched the new charger that is lithium rated to the old one that I'm removing - both charge at a max output of 55 amps.
2020 Heritage Glen 22RBHL