I'd suggest "measure twice, cut once". Install a battery/charge monitor
, which you will need regardless of what system you finally go with. See how long you can go with the two AGMs you have, at a 30-40% depth
of discharge. Maybe even 50%. In the worst case you will just use them up a bit faster (at 50% compared to 30%) and you'll have used
them, as opposed to tossing them.
Given that the east coast
is not the tropics, your fridge may not be a killer load. So again, what you've got may be good enough for now. Do an inventory of your electrical
loads and see what is taking power. You may find, as many others have, that simply replacing all the lighting
(nav & interior) with LED lights
cuts a tremendous amount of power use, and pays for the expense of the conversion.
On the windlass
, check the wiring
. On a boat your size there may be 100' of cabling (round trip) to the windlass
and the voltage drop in that can be huge. Or else the cable cost is huge. Whether you choose to put a battery
forward could depend on whether the cabling is adequate enough not to.
What to do with the AGMs, whether to keep them, repurpose them, etc., are all a bit premature until you know how well they might do the existing job.
And if charging
them from the engine
from time to time is part of the picture, there's also the question of optimizing that charging
system, using a continuous-duty alternator
and external regulator
. Which again would be something you want regardless of the battery
solution you choose.