We were in a very similar position when we bought out Moody 31 which came with 2 x 110AH batteries. These were joined together to create a single 220AH bank and a new separate Redflash AGM
fitted out of the way for engine
starting. Tiny little battery with lots of umph.
Next we bought a Honda
20i, seems we pay in £ what you guys pay in $
Kept the Honda
for 4 years because in addition to charging
it provided electric
for the calorifier
hence hot water and mains electric for heating
in the Spring and Autumn (we are 50.N). This worked quite well until we fitted diesel heating
at which point the Honda wasn't used anything like as much.
Then came two solar panels
totaling 125w which combined with a bit of work reducing out electrical
demand easily meets the need during the summer at anchor
. We use 30-40AH a day including fridge, lights and laptops etc. Indeed the first summer I was wandering around the boat looking for things to charge up by mid afternoon to make use of the spare power when the sun really shines. Our longest test was 5 days at anchor and we left with full batteries.
Sold the Honda 20i for nearly what we paid for it and gave up up on hot water unless we run the engine
or boil the kettle. Lots more space in the cockpit
locker now too.
So what's next? well another solar panel to take us up to 200w or so, to cover the possibility of a rainy week during the summer, probably loose and just placed on the deck
in a frame at anchor. At sea we use more power with autopilot
and lights etc, but don't mind running the engine for an hour during the night just to keep on top of things. If you are in the NE then don't forget you have alot more daylight in the summer than those further south. Oh sure the panels won't give full charge at 5am in the morning but they are working and will still be working at 10 pm as the sun sets.
One thing to think about, we did a 14 hour channel crossing under engine because it was flat calm. As we left we needed to add 30 AH to the 220 AH bank. Took the 60 amp alternator
10 hours to do that, because nearly full batteries will only take a tiny amount, though advanced charging
with a new multi stage alternator will help a bit. Just not convinced that you need a 100 amp unit, what you need is the higher voltage to charge the batteries quicker so 14.9v instead of say 14.2v which you could have from a smaller 75 amp unit saving on the twin belt requirement and a few dollars.
Sort the charging out and you may not need a 300 AH bank or it could be added later if you did. First thing though has to be a battery monitor
regardless what ever else you do so you don't spend hours charging if it isn't required, been there.