Within a given battery technology there is no practical difference
between two sixes in series and a twelve of the same capacity -- in
either case you have six two-volt cells, connected on top. With the
sixes, one connection is external, so you have to maintain two more
terminals, but you get to handle half the weight at a time when
replacing them.

Heat dissipation is a function of surface area, so I suppose if you
took two sixes and separated them by a few inches you might do a
little better. I've never heard of anyone doing this, but many larger
vessels have an exhaust fan on the battery box. The reason it's
required is to vent hydrogen, but it probably also provides cooling.

As for the logic, "if one battery goes, it is much easier and cheaper
to replace", that's BS. If you lose half a battery set, you have to
replace both -- never mix battery types, sizes, or ages in a set.

This comes down to a price and form factor decision -- whatever fits
in your available space that has the capacity and quality you need.

And, BTW, the choice isn't limited to sixes and twelves. Rolls, the
top US marine battery manufacturer, makes fours and eights (for those
of us who run 24VDC) as well as sixes and twelves.

Jim Woodward
www.mvfintry.com

(Kneafsey Mike) wrote in message . com...
We are presently having a new boat built in South Africa. It has been
recommended that we use Trojan 6v rather than 12v for our house
system. The logic is that if one battery goes, it is much easier and
cheaper to replace.

Everyone says it is the correct decision, but one person mentioned
that the batteries don't do well in the heat of the Caribbean due to
the inability to disapate heat while charging. One person said this
was pure BS.

Thanks,

Mike
www.sailingthecaribbean.com