hmmm, maybe the Solenoid itself is buggered, but you said that changing the connection did fix the problem. Where are you measuring the voltage drop? At the battery terminals?
If i were you, I wouldn't put my batteries on the charger at all in the summer, or only once and a while if you aren't sailing regularly. Especially if they are new. If you are getting out on the boat, the half hour or hour you might run the engine will charge the batteries sufficiently to maintain.
Additionally, you should always start your engine with the batteries on "both" if you need to charge the house battery too. I don't believe our stock battery selectors are the anti-surge type so it is really hard on the alternator to move the switch when running.
I am thinking the solenoid might be my problem_but after reading all of the information in this thread I now have a few other things to check first_..negative lead from the engine block to battery_.the batteries themselves (mine are not new and always on an intelligent charger) inline fuses not to mention check all connections as well. Apparently the last owners put a new starter in at least and the ignition is now replaced so at least two things I can cross off the list. Thanks for all of the suggestions_.
