Condensation, you need a heater in the bilge.Remember the warm nov.dec.and jan, I had my bilge heater off, and went to the boat in Dec, holy sh-t the motors were drenched.... Fired up that heater and even now no moisture.....
Corrision on batteries.... not sure, but if I had no charger running all winter and no heat, I would yank them. At the least, I would disconnect them. Even when your battery switches are off you are drawing power from your CO detectors, not good for the battery.
I will be down at the boat tommorow, hopefully all day...
Walter