Bruce-
1) usually a nominal 12 volt lead acid battery is concidered to be fully
charged at 12.7 vdc (measured after 24 hours of no charge or discharge).
12.70 vdc= 100% charged
12.45 vdc= 75% charged
12.20 vdc= 25% charged
11.95 vdc= dead.
You might want to recheck your take of the system........if your two "cabin"
batteries were actually wired in "series", why, that would mean 24vdc being
supplied to whatever is connected to them...........!!!
Probably you are looking at a parallel connection (one batterys + terminal
wired to the other batterys + terminal, and the - terminals likewise wired to
each other) That way the voltage is 12vdc same as always, but your potential
amperage is doubled.
And your inverter that you "never" use probably functions as a battery charger
when 120VAC is connected. If the proper switches are thrown. Do you have any
paperwork what came with the boat? If so, reading it again may help.
Without looking at your boat I can't help, but you need to take a basic
boating electrical course.
Good luck
Mike

sez Bruce" ...I have a Maxum 2400 that has an unusual battery set up. I have 2
starting
batts on a 1-2-both-off switch, and then there are 2 deep cycle batts
connected to a power inverter in the cabin. I have learned that this is a
"poor mans gen set" set up. All batts were new last year, but now the 2
deep cycles are dead, showing 12.5 volts. What i cant figure out is how
they were to be recharged in the first place. They are connected in series
to each other with NO other connections to the engine/charger area. THe
starter batts both are connected to the battery recharger and have little
orange wires from the charger to the pos terminals. So my question is How
do I figure out how these batteries were to be recharged, do you think they
are dead since they have sat since the winter w/o a charge (I was just
assuming they were being charged by something, and we dont use the inverter
ever) We get near 14 volts when running, and the starter batts seem in very
good condition. Any help is apperciat..."