Ok Donald ..... Start with the simple stuff. Fiberglass, take baby powder rub it on your arms heavily,it will keep the fiberglass from getting in your pours and minimize the itching Now. To your problem ... It is hard to diagnosis an issue so far away. Start the simple stuff. Corrosion etc. If that does not fix it, then you go back and start from the source.
Sometimes batteries will show a 12 v surface chrg and have a bad cell Put a load on it your voltage will drop out.
I would suggest you take all 3 batteries out of the boat and take them to auto zone, napa or whoever and have them load test them. That's where I would would start.... Let me know how it goes..........your friend in CUP........