I highly don’t recommend replacing the house batteries with lithium unless you have made some major changes. Depleted lithiums place much more load on a stock alternator. And a DC to DC converter would have to be so de rated that it will take a long time to charge. I suggest that you leave your stock alternator alone and let it handle the starting LA battery and thruster battery. Fabricat/purchase an bracket for an auxiliary alternator. By selecting the appropriate Balmar alternator you can charge at extremely high current if necessary and it can be set as to not over whelm the engine power at maneuvering speeds. Lots of options.
As of late I’ve found less needs to enhance house battery backs since LED’s (converting to) have shown up everywhere. More popular now is an auxiliary alternator 48v (55) that just charges an inverter battery bank, leaving the stock alternator to charge the original size starter, house, and thruster LA batteries ( any top brand AGM).
