Install
Do Boats Need a Separate Starting Battery with Lithium?
Yes, unless your engine builder has approved lithium starting in writing. It is a warranty question before it is an electrical one.
Do Boats Need a Separate Starting Battery with Lithium?: explanation
Keep the cranking battery lead-acid and keep it separate. It is cheap, it is proven, and it means a BMS disconnect on the house bank does not leave you unable to start the engine.
Charge it from the same alternator, and let the DC-DC charger feed the house bank from there.
More on install
Where does the battery shunt go?On the negative, between the bank and everything else — every load and every charge source on the far side of it.What fuse does a lithium bank need?Select fuses by circuit voltage, cable capacity, load and available fault current. Class-T is one option; suitability depends on the fuse’s actual DC interrupt rating and the system design.Does a lithium battery compartment need ventilation?The compartment must meet the battery and equipment installation instructions for heat, clearance and fault conditions. LiFePO4 does not normally produce hydrogen during charging.