[C320-list] Starter Battery and Fuel Tank Question and Parts3Engines.com Warning

[Troy Dunn]

Jeff

Your original wiring most likely had the charger directly wired to the
positive side of both the forward and aft 4D batteries underneath the salon
table seats on the starboard side of the boat.   I have a simple diagram of
the original wiring for Hull #514 in my photo album under DC power
upgrades.   If you still have the 1/2/OFF/BOTH battery selector then it is
highly likely that you still have both charger cables running directly to
your house and “dedicated start” battery.  More on the “dedicated start”
thing in a moment.   But first....

There are many approaches to gaining a larger house bank, and or saving
money on less battery capacity while still maintaining some sort of reserve
capability.   I have a diagram of my DC upgrade loaded to my album which
shows a bank of 4 GC2s providing 460 Ah at 12V and an additional 105 Ah
Group 27 reserve.   That is one way to gain significant capacity while also
having a reserve.

You can come up with many variations on this theme, to include a small
house bank of less than 200 Ah and a cranking battery as your “reserve”
(again with the quotes)   This might be totally fine for the day sailor
with limited overnight cruising plans and not too much in the way of
electronics.  That all boils down to your own personal preferences etc.
Bottom line, you probably just want to replace your very old battery with a
new one and move on.

The only thing I would want you to think about prior to replacing your dead
battery is what that battery is actually doing for you.  It’s wired through
a 1/2/BOTH/OFF so it is not actually a dedicated start battery.   That
requires a different switch and a different configuration of wiring.  What
you actually have is a reserve battery that you hope to have if you deplete
your house bank to the point you can no longer start the engine and or run
other electronics.   Some will suggest that you want a starting battery.
My personal preference runs contrary and is more in line with what your
Yanmar manual says.  I prefer a true deep cycle battery in that reserve
position, it will have thicker plates and be more durable over the long
haul.   Yes it will have less CCA than a thinner plate battery of
comparable size, but a group 27 deep cycle is still way overkill for
starting a 3 cylinder Yanmar engine.   Yanmar says minimum of 70 Ah, Group
27 is 105 Ah.   Bonus, when you eventually do need this battery and forget
to switch back to the house battery, running it into the ground won't mean
a highly degraded State of Health (provided you bring it back to a full
state of charge on the immediate charging cycle).

Also, you can get away with your reserve battery being slightly different
chemistry than your house, AGM vs FLA.   But I would avoid it.   Other
chemistry mixing is a no no without significant investment in additional
chargers since the differences in bulk/absorption/float voltages become
problematic with a single charge controller.   Not worth the investment.

Finally the batteries in your house bank should all be same size and age.
This is not required for your reserve.   It can be a different size and
age...hopefully new.  You do not need to run out and buy a new house bank
because your reserve is dead.

Regards

Troy Dunn
S/V Wonky Dog