[C320-list] Battery Cable Size

[Dave Hupe]

 I have just upgraded my boat's original battery charger (NewMar 50 amp) to a Promariner Pronautic 1240P (40 amp) with a remote panel.  It seems to be running great (and not running hot like the original charger, which bothered me a lot although it didn't cook my batteries).
In the process of doing all this, I have investigated my compartments more and discovered that a previous owner replaced the original 2 positive battery cables and the negative cable with much heavier ones.  The original cables were cut off and left in the wiring channels,  and replaced by 1/0 AWG cables.  However, instead of running straight positive cables from the starboard batteries to the port side battery switch, the new cables were joined/bolted together (at lugs on the ends of each cable) under the flooring (in the widest bilge area) and taped over.  Moreover, the positive cables started appropriately as red cables at the batteries, but were both joined to black cables that ended at the control switch. I don't understand why the previous owner did this, except possibly he used preassembled cables that already had wire lugs on them. 
Obviously, the bolted together cables are not a good idea (especially in the bilge area). So, I intend to replace these positive cables with straight runs from each battery to the #1 and #2 switch terminals. Each run is almost 17 feet long. 
My question...….is 1/0 AWG battery cable a good/proper size?
Dave Hupe
1994 Cat 320 (#32)
Holland, MI