Grounding Batteries

Thread Starter


Joined May 27, 2008
What's the best way to ground two sets of twelve volt marine batteries used to power a 16 ft. pontoon boat. Each set consists of two batteries connected in series to separately power two 24 volt motors. It was suggested that I connect a wire from the negative output terminal of each battery set to the steel motor mounts. Is this the correct way to ground the batteries? Also what would happen if I did not ground the batteries? Please note that the boat has a dual system to start and control both motors.


Joined Apr 20, 2004
Without having the wiring diagram, it's hard to answer sensibly. Certainly, though, grounding both batteries if connected in series will short one out, leading to some major problems.

Unless there is some overriding need, it is probably safe to let the batteries go unreferenced to the hull. If one of the motor terminals is tied to the hull, connecting the batteries will also ground them properly.


Joined Jun 10, 2008
I'll go out on a limb here....with one battery terminal tied to the [metal] hull, wouldn't this polarize the hull? I'm saying that may be a bad idea, electrolysis & all that stuff. Might not show up for some time.


Joined Apr 20, 2004
There has to be a path for current in order to get electrolytic effects. Most aluminum boat hulls have zinc sacrificial strips attached to circumvent the problem.


Joined Apr 27, 2007
You should use the hull as a negative chassis ground. Otherwise you make corrosion a even more serious possibility. Besides, like beenthere said, you can use zinc strips. A hull connected as a negative chassis and with zinc strips attached may avoid corrosion due to redox mechanism.

Of course, if you use the hull as a positive chassis ground you may not get more corrosion. But you will surely get some if something negative in the same circuit contacts the water as well. The negative chassis hull avoids that remote possibility. The zinc strips are the ones actively minimizing corrosion since they are already placed inside the water. Thus any redox reaction happens on the zinc strips and not the hull, since an electron flow going to the hull will compensate any electron loss on it, preventing redox reactions on the former.


Joined May 16, 2005
I thought "hull polarization" only took place in space operas.:confused:

Corrosion of the hull will be exacerbated only if there is current between hull and water. This will only happen if the wrong battery lead is tossed overboard. Very unlikely, that.


Joined Jul 17, 2007
Dissimilar metals below the waterline, particularly in brackish or saltwater, will cause electrolytic action to take place; in effect, a Voltaic pile. Material will be transferred from the more negative to the more positive, sort of like electroplating, but far uglier.

A good sized chunk of zinc, or several smaller chunks of zinc, will serve as "donor" material, since the zinc will be at the most negative potential. You might be surprised at how quickly they get eaten up.

One good place to put them is to bolt them to the anti-cavitation plate of an outboard or I/O drive motor; one on each side. The motor is one of the most expensive pieces of equipment on board; it makes sense to protect it.


Joined Apr 25, 2008
Search google (Eric Steinberg-Farallon electronic's)
Then click on (Pcup ssb-in 6.5,) you will get 11 page's
of grounding information.I googled the name ,the information
is there.This is the second time in recent week's that this
information has been requested. When I saw pontoon
I was thinking rubberized material.
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