Outboard engine battery setup

[drewpster]

I need to put together a good battery setup for my tri-hull project. I need provisions for a radio and a trolling motor and maybe some lighting. Other than that the electrics are pretty standard. The trolling motor is a 40lb. thrust model. I was thinking of using a single start battery and a single deep cycle. I want to use a manual battery switch as well as a means to combine the batteries automatically. (if that is recommended for outboard setups) I am not a fan of diode isolators.
Since the none of the accessories will generally be used all at the same time, I was thinking of setting it up so that the start battery is isolated for starting only. I will run all the "house loads" off the deep cycle. During fishing, the trolling motor and maybe the anchor light will be all that is used at a given time. Am I on the right track here? The big question is how, or should, I combine the batteries while the engine is running. The manual switch will be used to transfer all loads back and forth as needed between the batteries. I prefer a system that combines and isolates the batteries automatically rather than keeping up with a manual switch. I am way too forgetful for that. Any suggestions? Should I combine a potentially dead battery with a full one on an outboard?

 

[Silvertip]

Re: Outboard engine battery setup

Another overkill project. First, what engine are you running? Know that most outboards in the under 90 HP range do not have enough alternator output to charge two batteries. To charge your deep cycle would mean the engine would need to run wide open for hours to accomplish the task. Why put low draw house loads on the deep cycle? Lights, radios, depth finders, bilge pumps, live wells all are not high draw items. Use the deep cycle for its intended purpose -- to run the troller and get the most time out of it. Use a marine "dual purpose" (starting/deep cycle) for the starting battery and enjoy the boat. Forget the switch and install a two bank on-board charger. Carry a cheap set of jumper cables or a jump start box if you are worried about running down the start battery.

And if you are trolling, the nav AND anchor light must be on because you are moving. The anchor light is on ONLY when anchored.

 

[drewpster]

Re: Outboard engine battery setup

Thanks for reminding me about the nav/ anchor lights. I have spent too much time on land these days.

Your right, going the way I suggested is overkill. As you know that is what I do.
I am running a Merc 90hp. I am planning on an onboard charger at minimum and a main battery switch for safety sake. (on/off only) I'll use the charger to keep the batts up.
I was also thinking about a permenent mount trolling motor plug to cleanup the install a bit. I also may want to remove the TM for safe keeping from time to time. (transom mount) We plan to travel with this boat.