Hey guys - I'm thinking about rigging a dual battery setup in my tri hull as part of a rewire. I know the old motors don't have very strong charging systems. Would the motor put out enough amperage to actually charge 2 batteries well enough make it worth the trouble? I would probably run all the electrical (lights, depth finder, maybe add a radio) off the house battery and reserve the main for starting only. This would be mostly a safety move since we like to anchor out and kick back while listening to the radio.
I know this is over simplified but as long as you're going to invest in a second battery get yourself a good deep cycle. Put it in your battery box alongside the main battery so that you can switch wires if needed. I have a separate wire system for all the extras, depth finder, radio, lights, etc. I run +/- wires from the extra batt to a buss bar under the dash and then connect the extras to that buss. You then have the option of using the main batt just for the motor or swapping with the deep cycle, or running the batts in parallel for longer life. I also have a cheap voltmeter hooked up on the extra battery wireing to monitor drain. Less than $10 on ebay, free shipping
A good deep cycle batt will last over a day or more if you're just laying back. When you get back to shore just put your trickle charger on it,