Antares 760 battery selection for engine and accessories.

[Tondi]

Recently bought a 2007 Antares 760 with electric windlass and bowthruster.
Just discovered that the 2 x 80Ah deep cycle batteries connected in parallel are connected to the engine starter, windlass and bowthruster!
The one very large automotive type battery is connected to all the domestic accessories!
These are surely the wrong way around?
Has anyone else found their boat has been wired similarly, or found a good reason for doing so?

 

[Plum]

Recently bought a 2007 Antares 760 with electric windlass and bowthruster.
Just discovered that the 2 x 80Ah deep cycle batteries connected in parallel are connected to the engine starter, windlass and bowthruster!
The one very large automotive type battery is connected to all the domestic accessories!
These are surely the wrong way around?
Has anyone else found their boat has been wired similarly, or found a good reason for doing so?

The more important factor is the CCA (cold ranking amps) rating of the engine start battery/batteries, not the Ah rating. If you ever want the domestic battery/batteries to be able to crank your engine then you need the same CCA for both banks. I have 1000 cca for both of mine so I can use either battery to crank. However Volvo Penta specify a 140Ah cranking battery assuming you have the TAMD41 engine

 

[Tranona]

That is correct. The battery size/type is matched to the pattern of demand. The starter, thruster and windlass all require high amps (CCA) and the domestics are slower discharge of lower amps over longer periods.