Just reporting back that I changed my two AGM group 31s yesterday with two new
AGM group 31s. I thought 31's were a little bit bigger than 27's. Either size
fits in my OEM battery boxes. I still have the original battery switch, "off,
one, both, two" so either battery can start or power the house loads. It's not
state of the art, but works. I can't justify the cost to upgrade to lithium.
The batteries are very close to AGMs now, but the extra controllers needed to
do a proper install push this upgrade to $2500 to $3000. I'll probably sell my
boat in a few years, so I won't give in to the lithium temptation.
I added a $120 Victron "smart shunt" which I recommend to others when replacing
batteries. This device reads the amps going through the negative back to the
battery, which wirelessly sends battery info to any smart phone, no display
needed.
Just for fun, I recorded all the loads in my boat, so I can better plan. It
verified that my fridge only uses 48 watts when it runs and the LED lights and
Canframo fans are super efficient. I still need to change a couple of
flourescent light fixtures that draw the highest amps, to LEDs.
Summary: If I lived on my boat, or planned to keep her for more than five
years, I'd upgrade to a Lithium system and add solar. Otherwise, I will use my
AGM batteries and might add a third AGM for more amphours when cruising. The
new batteries were 72# each, ugh.
Chuck Scheaffer, Resolute 1989 C&C 34R, Annapolis
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