Should bow battery bank share negative with starting battery?

[jplomeo]

Hi Folks,
Thanks to all who share their knowledge and expertise on these forums!! I have a silly question: I have just installed two deep cycle batteries (same size, make and age-wired in parallel on the bow ) for the 12 volt trolling motor on a 17 ft crestliner (aluminum) for additional trollling run time. Should I be running a cable to hook up the negative of this front bank to the starting battery negative in the back by the outboard? And If so, what size would be adequate for the 17 feet distance?

Thank you so much!
JP

 

[MrGiggles]

No, there is no need. They can be completely isolated.

 

[C&K]

The only reason to hook them together is if you want to run a charging circuit from your starting system, charged by the alternator on the outboard, to the trolling system. We have this in our Alumacraft Pro 17 and there’s a switch on the panel that connects the two battery systems. In our boat the starting battery powers the nav lights, deck lights, radios and electronics. If we’re out walleye fishing at night the trolling motor bank has more power than the starting battery, so connecting the two with the switch takes the load off the starting battery to power the rest of the boat. And also charges the trolling bank with the outboard when it’s running.

So there is some valid reasons to be able to connect them together. But just the ground wire by itself between the two will accomplish nothing.

 

[jplomeo]

Thank you Sirs,
That it kind of what I thought, that it was not necessary. Thank you so much for confirming that. I did once have a battery isolator system to charge the trolling bank from the outboards alternator, but my style of fishing is mostly a lot of trolling and very short runs with the big engine, so I did not get to charge the trolling bank enough to make much difference.
Tight lInes!
JP

 

[airshot]

On my small boat, I have batteries for everything, hate the thought of running out of power when I need it !! Two group 31 bats for the TM with there own onboard charger. Then a marine starting battery with its own onboard charger along with charging from the motor. Then I also have another gp 31 house battery to run the boat lights and electronics with its own onboard charger. Can be out trolling all day (8 hrs) with all the electronics going and even nav lights, have never run out of power and when I get home, one plug runs all the chargers so I am ready to go the next morning !!