Recently purchased 450 Voyager with twin Cummins 450 Diamond Series. Port alternator went out so checked starting batteries and all are shot. The boat currently has the following. All batteries are identical AGM31M, 1150 CCA.

Each engine two 1150 CCA gel batteries in parallel

House has two 1150 CCA batteries in parallel

Genset one 1150 CCA battery

Bow thruster 24 volt so four 1150 CCA batteries in series

So my questions are:

1)Cummins specs call for I think 1100 CCA each engine. For boat operation (local lake) in temps above 60 degrees F, do I need two 1150 CCA batteries in parallel each engine or is one sufficient.

2)For the house batteries, do I need 1150 CCA or can I go lower since I’m interested in lasting time instead of cranking amps.

3) Bow thruster is rarely used on local lake. Can I drop back to two, 12 volt batteries in series instead of the current four batteries?

Any advice is surely appreciated.