Hey guys, i have a situation that im hoping someone has a little insight on. Let me give you some background info, i have 2 batteries in series for my 24v trolling motor, and i have a 3rd battery by itself that runs most everything else on the boat as well as starts my engine. Now, recently i added two helix 7's and a stereo to the boat. After 4 hours or so of fishing and listening to the radio without having run the engine, i killed my starting battery. I have a 3 bank Mk onboard charger as well. I am trying to come up with a good way to add a deep cycle battery to the boat to run my stereo and fish finders. I would like to be able to charge this battery with the engine, and the onboard charger if at all possible. The battery switch seems like it would be a pain to worry about switching batteries all the time. Can i add a voltage sensing relay inbetween my starting battery and this new auxilary deep cycle, and just keep on running the way ive always been? 

If it ran down in 4 hours I would think that battery was on its way out to begin with. What are the CCA of the starting battery ?

You should have circuit breaker for each individual 12V battery and a battery switch to off/on the cranking battery to the outboard when charging at home. Sounds like you need fresh group 27 or 29 for your cranking battery and other electronics, no reason to isolate the stereo unless it has high amp power. You may need a jumper cable!

Tom

I dont remember the CCA of my cranking battery right off the top of my head. I do have breakers but no battery switches. This is on an older procraft. Not sure if it never came with them or if they were removed at some point. My stereo is nothing crazy, alpine deck, 4 channel amp, and two 6x9 speakers. I do understand the point of a battery switch, but the reason i was thinking the relay would be nice is because it would automatically cut the deep cycle away from the cranking battery when the motor is not running, without having to flip the switch. Am i wrong in thinking that?

Switch or relay both would isolate the OB from the cranking battery. Your OB should have a relay for the alernator charging the cranking battery as needed when running, not sure about what you have?

Battery switches are usually a option that's added on by the boat owner unless the boat was rigged professionally.

Nice Brittany.

Tom

Thank ya sir, best dog i got! Anyway, i went with the switch option. I think i was looking to far into it before. I was thinking i would have to be throwing the switch all the time but now that i think about it, thats kinda dumb. I got the switch and my minn kota 3 bank on board charger installed tonight. Thanks for the help.