You are correct. With two pairs of series-connected 6v batteries, the
current across the companionway will be half of that with two pairs of
parallel-connected batteries.

There will be losses in the 4/0 cable when you load the bank, of course.
At normal charging currents, the voltage drop in the 4/0 cable will be
insignificant.

A further advantage of 12 volt banks P&S is that each can be used
independently in the event of a problem. Not so easy with two 6 volt banks.

The advantages of two 6 volt banks are not immediately obvious to me.

Chuck



Glenn Ashmore wrote:
I have four L16H 6V batteries for my 840AH 12V house bank. Due to space
and balance limitations two are on the port side of the companionway and two
on the starboard. The fuse, battery switch and power connections are on the
starboard side. I am running 5' of 4/0 cable between them. It has been
recommended to me by several people that I parallel each pair and then
series across the companionway. That does not seem right to me as it would
put the full amp load at 6V on the longest cables.. I am thinking it would
be better to series wire each side so the longer cables are carrying 12V and
half the amps

Am I missing something?