My call to Battle Born stated that I should not use a 100Ah BB to start a D6 Volvo. But using the combining switch to connect the 4 Lithium house batteries to DEAD lead acid is fine to occasionally start a dead start battery should the lead acid start battery die. Just don't do it all the time.
As others have stated, the ARC won't disconnect start/thruster due to voltages.
The ACR can be replaced by DC to DC battery charger. The DC charger will sap power from the charging Lithium at a higher voltage, and step it down to the proper voltage to charge the lead acid start and lead acid thruster.
I wonder if you don't start and stop you boat but once a day, can you combine all 6 lithium for over 600 amp hours of power to start a engine if that is bad for a battle born battery? Then you can get rid of 6 80lbs batteries and replace with 6 30lb batteries. That would save 300 lbs, the weight of a 100lb dingy, 100lb outboard, and 100lbs of junk.
Also, don't forget that most lithium drop in batteries have a built in BMS, battery management system. When they are full, the BMS disconnects the battery. If all lithiums in a "all lithium" bank turn off, the alternator will spike its voltage and burn out diodes if voltages goes infinite and amps go to zero.
