In a setup with batteries in series just one failed cell will bring the whole system down. Identify it/them and replace. Don't throw them all away just yet. See Nigel Calder's Boat Owner's Mechanical and Electrical
On the water
in the bilge
subject, you have a hull
to keep the water
out. If there is water inside it find out why and stop it. IMHO bilge
pumps are there to buy you minutes in an emergency
. My bilges are dry except for the one where I dump the condensation
from the aircon, which works only when I am on board.
Above all, best of luck and tell us what you find.