Thread: Wiring a battery swich to to have two trolling motor batteris. Wiring negative side?

I would think you would be ok,That type of connection is used in some makes of automobiles with there trailer and brake lite hookups,my ford windstar used it Its called low side switching for me it was a nightmare.because the frame was grounded.and i wanted to hookup a boat trailer for lites etc.but still I think you should be ok because your grounding is not connected to your boats hull...

Originally Posted by helpme

I would think you would be ok,That type of connection is used in some makes of automobiles with there trailer and brake lite hookups,my ford windstar used it Its called low side switching for me it was a nightmare.because the frame was grounded.and i wanted to hookup a boat trailer for lites etc.but still I think you should be ok because your grounding is not connected to your boats hull...

Thanks for the reply. I switch to off and hit the breaker while storing and charging. I charge each battery independently with two separate chargers. I was worried that something funky could go on with both positives connected together while charging, but all of my electrical knowledge tells me that I should be ok since the negative terminals are isolated from each other.


I figured it was better to run the batteries separate instead of a pure parallel connection, in that I didn't want one battery to maybe drain at a different rate and deter the performance or lifespan of the battery.

Originally Posted by JAW1973

Thanks for the reply. I switch to off and hit the breaker while storing and charging. I charge each battery independently with two separate chargers. I was worried that something funky could go on with both positives connected together while charging, but all of my electrical knowledge tells me that I should be ok since the negative terminals are isolated from each other.


I figured it was better to run the batteries separate instead of a pure parallel connection, in that I didn't want one battery to maybe drain at a different rate and deter the performance or lifespan of the battery.

It makes no difference whether you switch on the power or ground side. The reason you disconnect ground side first is for safety, since the body/chassis is typically grounded in most applications.

You cannot unevenly discharge batteries in parallel, if the batteries are of equal age and capacity.

It would be better for the batteries if they were just left in parallel and discharged/recharged at equal rates, rather than sucking one down and switching to the other. Also less things to monitor, however you wouldn't have a battery left in reserve.

Parallel is the way to go. Simple and it minimize depth of discharge. Charge them in parallel and run them in parallel.

Originally Posted by CatFan

Parallel is the way to go. Simple and it minimize depth of discharge. Charge them in parallel and run them in parallel.

Been doing mine that way for years.

Originally Posted by DockShootinJack

Been doing mine that way for years.

Mine too I have fished all day and never pulled the two in parallel down very far


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There are just some things that not all of us will fully understand.
So for me at least i either hire someone who does, or i use the Kiss method.
My current go to boat is a plain Jon boat with a battery in the bow for the trolling motor.
And another in the stern for starting the outboard.
They are not connected together.
I have a 2 bank charger, one lead goes to the bow, and the other goes to the stern.
I have never used up the trolling motor battery on a trip, but if i did i would just go home, or change tactics.
Life is good, and even better for at least some of us with the Kiss system. lol

This is parallel. And it is simple

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