C_Spray
Charter Member
I've had good luck with Deka (East Penn Mfg.) combination deep-cycle/cranking Group 31's. This is the brand of batteries Formula usually supplies from the factory.
I use one for the port engine and two for the house bank/starboard engine. They tolerate discharging to low voltages like a deep-cycle, but still provide LOTS of cranking amps. Each system runs independently off of that particular engine's alternator, but can be combined if need be. Using all the same spec batteries keeps life simple from the charging standpoint as well - you can use the same settings on all the alternators and battery charger(s).
Remember, if you convert from flooded to AGM batteries, you'll have to re-adjust everything. AGM's charge at over 14 volts....
I use one for the port engine and two for the house bank/starboard engine. They tolerate discharging to low voltages like a deep-cycle, but still provide LOTS of cranking amps. Each system runs independently off of that particular engine's alternator, but can be combined if need be. Using all the same spec batteries keeps life simple from the charging standpoint as well - you can use the same settings on all the alternators and battery charger(s).
Remember, if you convert from flooded to AGM batteries, you'll have to re-adjust everything. AGM's charge at over 14 volts....