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Onboard Charging


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Started a new thread concerning onboard charging.

My "new to me" boat has a noco 4 bank charger that was connected to the 2 trolling batteries (dc group 27) and a cranking battery. Although I love the idea I was having problems with my trolling motor batteries so I took the charger out of the equation to find the fault. I replaced the trolling motor connector and the problem seems to have disappeared making the assumption the charger is fine.

Is there any CON to re-hooking up the onboard charger? I'm always paranoid that since the trolling batteries are connected in series (24V Terrova) that this might confuse the charger even though the batteries are connected separately to the charger.

Also, the boat also has a "House" battery that could also be connected to the charger but is not. Is there a reason it wouldn't be? Actually, the charger is missing the 4th cable that I have find (no luck yet) and purchase.

I will add a wiring diagram later but it's nothing to crazy. It does include a (2+1) switch for the Cranking and House battery...

Any thoughts welcome, thx.


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I can assure you that the noco genius charger has no issue with batteries in series. be it 24 or 36 volt, the charger has no concerns charging individual batteries as appropriate. I have heard that one should consider ensuring that their trolling motor is shut off when charging. Im not sure I have ever headed that advice. When i pull up to the dock the boat is plugged back in, every time.

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I agree with Akr, I've had several boats with OB chargers, both 24 and 36 volts. Each bank of the charger connects to each battery's respective +/_ regardless of the final voltage. Also, I would connect the house battery to the charger as well otherwise how is it getting charged?

Regarding the state of power when charging, You can charge with the power either on or off. Most of us turn off the main power (cranking and house) and the TM batteries. There should be a circuit breaker on the positive lead to your trolling motor.

On reason your 4th bank is not connected - there may be a charging relay (combiner) that automatically switches between the cranking and house. Also called a "combiner". Google this and have a look at them and their associated wiring diagrams and holler back if you need anything else.

One last thing when working with DC power. The amount of energy in these batteries is huge so be very careful when connecting/disconnecting as not to short out anything. To give you an idea, household current is 15amps.  Each of your batteries will be north of 650amps.


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Thanks for the input guys.

I have been "topping up" the house battery before every trip because the sonar beeped once or twice that voltage was low. Went and checked today trying to sort out everything and noticed the "2+1" switch was on "1", the cranking battery. For some reason I thought it was on "BOTH" allowing the engine to trickle charge both the cranking battery and house...

OK, that may be solved now, slowly getting a handle on my "new to me" boat.

Next I will grab the 4th bank cable to be able to charge all 4 batteries on dock...

Getting there...

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20 hours ago, BillM said:

What finders do you have on your boat?  Stock wiring leaves a lot to be desired.  I was constantly getting low voltage alarms on my Helix 12s until I ran dedicated wire from the house battery to a distribution box and used that to power both my graphs.  

Theres even some debate about that depending on the length of the run to your distribution box. Typical installation from guys like Sonar Pros now involves running a short heavy guage (4awg) run to a shut off, and then running clean 10awg runs to each graph in the boat. Even doing that I still have noticeable voltage drop between the bow and helm of my boat. Can never have enough juice running to those units.


A single helix 7 should have no issues at all, they draw hardly any juice, its when you start going stupid with 3+ 10+ inch screens running panoptix and networking blah blah blah. 


I had to install a Automatic Charge Relay in my boat because my designated electronics battery a Group 31AGM wasnt getting my through some long days. Stupid stupid stupid lol ahhh the games we play.

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Purchased another set 10' bu will have to extend 2 feet, no problem I have proper gauge, heat shrink etc. will do a clean job but...

I'm still wondering why a boat with a 4 bank charger wouldn't bother with the house battery.

I have a thought (could be wrong). What if 2 were run to the trolling motor batteries and 1 run to the crank BECAUSE with the switch at 2+1 basically the crank and house are in parallel so only 1 could do the job.

Ideally a bank per battery is right, I get it, but maybe that's why they didn't add the house directly to a bank.

Or..Maybe that bank on the charger is toast..

Its a NOCO G4 with 1.1A per bank so basically just a trickle charge... Will probably put my Noco Gen2 20A eventually on the boat but its only 2 bank.

Boy this fun!



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Isn’t trying to figure out what the heck the previous owner of your boat did with their wiring fun? Lol

This is why, since I’ve owned two boats now, each one has gotten close to essentially total rewire. 
gremlins appear and it’s typically because the wiring was not done right the first time.

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