Re: Adding a second battery........
I added a battery to my boat a few years back, and I'm glad I did. When yer primary one fails, it's very reassuring to know that you've got a fully charged spare.
http://bluesea.com/category/78/1/productline/overview/329
I used battery cables purchased at an Ace parts store, and wired them to the above switch. It comes with a relay that allows both batteries to be charged serially (only charges the aux battery after the primary is fully charged). The arrangement allows only the aux battery to be drained for aux equipment (music, GPS, finder, etc.) while the motor is not not running, thereby keeping the primary charged for starts when needed. With it, you can drain your aux, but not your primary. The arrangement also allows you to gang your two batteries if needed in an emergency.
When yer out on the suncoast fishin' or playing off of Hernando Beach, you won't need to keep Tow-Boat US on speed dial. ... Stay out'a the sun...