My house bank is lithium and both starter batteries are AGM. I have Balmar regulators and centerfielders on alternators to charge the house. I was going to use a Victron DC to DC charger from the house to charge the AGM starter batteries. Do I need two DC to DC chargers or can I use one paired with victron cyrix combiner to charge both? Could there be issues with battery isolation during starting? - Reason
With two separate AGM engine battery banks, you’ll definitely need one DC to DC charging converter per engine battery bank, therefore you’ll need two DC to DC charging converters connected to your lithium bank.