I need a battery education. I have C30 with to banks of batteries. 1 is for starting and the other has two batteries for the house. I tried to start the motor last week after the boat had been sitting for about six months and it was dead so I switched to bank 2 and it started up. The boat is plugged into shore power and has the fridge running all the time (need cold beer to work on the boat and the power is no charge). I checked the starter battery and the positive post corroded right offuke so I need a new starter battery. All the batteries are Gel. Any advice?