Category Archives: Battery Management

Shock Absorber


I’ve heard in the past and as recently as last night that “dc won’t shock you”.

Well, I’ve grabbed a plug wire at the plug and can report to you that the DC electrical system is standing tall. I had a brain fart prior to grabbing that wire.

Electrical shock hazard

But as to the truism, maybe I am missing something? What are these people talking about?

Please explain.



As you proved through your careful experimentation, DC can shock you. The determining factor is whether or not the voltage is high enough.

Boats run on 12 volts (some at 24 volts). Your internal resistance is too high to allow for a noticeable discharge through your body. But, on an ignition system, the DC voltage can be as high as 30,000 volts. (2,500 times as high as your normal boat wiring). It is easy to discharge 30,000 volts DC or AC through a body.

Hope this helps to clear things up.


Trolling Plug Work Around


I am in need of your help with my boat's 24 volt trolling motor wiring.

I have a problem using my 70 lb. trolling motor at full power. It shuts down and I cannot use it.

Marinco trolling motor plug

The motor is wired using a Marinco 24 volt plug and receptacle. I talked with Marinco at one time and they told me the jumper in the plug was under sized but they had no corrective parts.

Any ideas of what has happened or what I can do to get this system running again?

Thanks for your help!


One option is to use only two of the terminals in the Marinco plug and do the 12/24 jump at the battery.

Basically, there is a wire from the plug to the negative of Battery 1 for the ground and a wire from the plug to the positive of Battery 2 for the 24v positive connection. This lead has circuit protection at the battery. A jumper between the positive of Battery 1 and the negative of Battery 2 is added to create the 12/24 system. This wire should be made from the same size wire as the long trolling motor leads.

Hope this helps,


Manitou Pontoon Boat Wiring


I am working on a 2005 22" Manitou Osprey Pro. Is there any source for obtaining a boat wiring diagram for this pontoon?

I just recently purchased this and have been trying to fix some electrical issues. Some are relatively straightforward.

Manitou Pontoon Boat

The pontoon's stereo speaker color codes matched the vendors color codes directly, but the stereo's power hookup did not - both yellow and red leads from the stereo were tied to a the pontoon's solid red wire. There was also a red wire with a yellow tracer in the same (stereo) wiring bundle of the pontoon but it was just clipped. Is one of the these a direct battery connection and the other one an on/accessory connection? The stereo wiring diagram shows two positive connections one labeled battery and the other labeled ignition - I don't want the stereo on all the time. The sun has faded all the indications of position for the ignition switch and all the switch/breaker functions. I don't even know if the ignition switch has an accessory function/position.

I don't know if the 5 function switch panel is a standard wiring. Is there a standard layout for the switches? Since the stereo speakers and power seem to follow the standard color codes for front -rear and power, is it safe to assume all the lights, horn and other accessories follow some standard of wiring? If so what are those standards and where can I find a standard schematic or wiring diagram for those standards?

I can't wait to get out fishing on this pontoon - it has an installation for a trolling motor battery in the console with direct wiring to an outlet mounted at the bow for the trolling motor (no battery installed yet) - there doesn't seem like a way to charge this battery from the engine's alternator/charger. Is there a way to connect this battery to the the engine's alternator but not allow the trolling motor battery to try to start the main engine? I don't what to run the higher gauge wiring for that. I just want to use the trolling motor battery for the trolling motor and accessories when the main engine is not running if that is possible.

I would like to develop a wiring diagram for this pontoon but I would hate to have to start from scratch and trace out the circuits by trail and error.

Any help would be really appreciated.


It sounds like a previous owner was doing some wiring modifications. We know the Manitou crew very well, and it is not like them to have hidden wires clipped off in their harnesses.

The key switch accessory position question is based on the brand of the engine on your boat. The easiest way to tell is to turn the key switch. It will either have 3 positions (OFF-ON-START) or 4 position (ACC-OFF-ON-START). If the key has an accessory position, it will have an A or ACC on a tab on back of the key.

There is not a standard layout for the switches on your helm. I would consider calling Manitou in Lansing MI to see if they have replacement panels for your boat that would have the proper labeling for the panels.

Here is the common boat wiring color code used by most OEM boat builders, including Manitou. You should be able to use this to trace down any wires on the boat.

If you want to charge the trolling motor battery while the engine is running, you will need to run some larger wires between the starting battery and the trolling motor battery. This wire size is based on the size of the alternator on your engine. Most VSR smart battery switch systems are capable of handling 125+ amps but the limit is the size of your alternator. If you alternator is less than 20 amp, the VSR is almost a waste of money. You will need to run your outboard at full alternator output for nearly 3 hours to replace what the trolling motor can draw in less than 1 hour.

Hope this helps,


Crestliner Wiring Upgrade


Could you please check out my homemade boat wiring diagram? It’s for my 17.5′ Crestliner Fish Hawk.

As you can see, I added and wired the two Attwood battery selector switches and a fourth battery to the system (Battery 2) and wired all the batteries in parallel. I also added the Blue Seas fuse block, all lighting, fishfinder, trolling motor, etc.

Crestliner boat wiring diagram

Click to Enlarge

My goal here is to be able to run the trolling motor off the extra battery if needed and/or to be able to start the motor with the extra battery if the main died. Also, to run all the lights off the extra battery for night fishing. I’ve yet to turn both switches to “both” because I’m not sure if that would be bad for……..everything.

I’m obviously an amateur at this so was wondering if you think it’s a safe setup assuming all the fuses, connections, wire gauge, etc. are kosher? I haven’t had any trouble yet but I’m a little nervous about burning something up.

I’d really appreciate your input if you can decipher the wiring diagram.




I would make a couple of minor changes:

  • Move the trolling motor circuit protection to the trolling motor side of the switch.
  • Add circuit protection for the Blue Seas fuse panel at its connection location to the boat battery switch.
  • Use the same size boat battery cables for all of your battery link wires. You call out 4/0 for the positive lead (I would assume you mean 4 AWG) but not on any of the other cables.
  • If the trolling motor batteries are near the bow of the boat I would consider adding circuit protection at each end of this wire to help reduce the risk of a catastrophic fault.

Hope this helps,



Thanks for the help Kevin. I’ll do all of that.

Also, I was wrong about the battery cable being 4/0, its actually 1/0 welding cable.
Thanks again,



Most people don’t use welding cable on boats or cars because it is not oil resistant.


Kayak Power

Hey Kevin,Motorguide trolling motor

Your site is amazing. Thanks for all the info.

Now here is my boat wiring question:

We have a Native 14.5 ft Kayak. It only weighs 75 pounds and wish to power it with a 12 volt Motorguide trolling motor on some of the quieter lakes for fishing.

What are the battery options? Will a 24 volt with 93 amp hours work? And for how long? From reading your posts I learned we need a better charger than the 25 year old trickle charger we have, any gems you recommend?

Thanks again.


Most of the time, you don’t want to discharge a boat battery below 50%, so you are only going to use 46 of the 93 amp hours available in the battery. The small, 30 lb thrust trolling motors draw about 30 amps at full power. At wide open, you can expect the battery to last about 1.5 hours. A 5 amp charger would take about 9 hours to recharge the battery after use.

Hope this helps,


Bigger Better?

Dear Kevin,

I have a Marinco 12-24/24-36 plug and receptacle installed on my boat for my trolling motor.

I have switched from a 24 volt system to a 36 volt system and noted that two of the four prongs on the male plug are larger than the other two. Marinco trolling motor plug

The trolling motor uses two wires (black and red) for power from the batteries. Should these wires be installed on the two larger prongs, since the 36 volt system will be drawing more current than the 24 volt system. The prongs are labled A+, B+, neg, and NET on the back of the plug.

Thank you for your time.


Hi Arthur,

I would use the larger terminals in the plug for your new trolling motor. They have more contact area and will be less likely to get hot during heavy operation.

Hope this helps,


Thanks Kevin.

That was my thoughts. Nice to have your take.


Trim Trouble

Hi Kevin,

I have a boat which is a center console.

When I give the boat’s engine direct power, it starts and the tilt trim works. But, when I connect the battery to the terminals, it’s no good – it won’t even crank over nor will the tilt trim work.

I have tested the isolator switch with a multimeter and it seemed to be fine.

What else do you think I should do?Marine electrical trim panel

Thanks mate,


Hi Ozzy,

Test the switch and cables with the engine connected while you are trying to start it.

It is very common for cables and switches to read fine with a meter, but as soon as you draw current down them, there is too much resistance in the wire/switch and the engine will not start.

Since the meter draws a very small current, it not cause the huge voltage drop problem that you are seeing.

Hope this helps,


Hi Kevin

So do you think I should buy and try a new isolator switch?



I would test the voltage at the battery switch when you are trying to start the engine. It may be the boat battery cables.


Bow to Stern?


I need some advice on the best battery configuration for my boat.

I have a 19 foot Blue Wave fishing boat with a Yamaha 115 and a 24-volt trolling motor. Currently, I have two dedicated trolling batteries mounted in front; cranking and all other accessories are handled by a single battery mounted in back. I also have an onboard marine battery charger mounted in front for the trolling batteries.Blue Wave 190

This setup works just fine, but I don’t like having the two trolling batteries and the charger in the front (space and weight distribution considerations). There is room for all three batteries in the back with a few minor adjustments.

So here are my questions:

  1. If I mount all three batteries in back, is it possible to set it up so that all three can charge from the alternator? And should I keep the configuration of two batteries for trolling and one for everything else, or do something different?
  2. Is there a simple and reliable way to do this with just two batteries?



Hi Jeff,

Moving the weight aft may not be the best solution. The additional 100+ pounds may cause the boat to be slower on plane and to porpoise at top speed. I would test the weight in the aft before making any wiring changes.

There are devices like the Guest/Marinco Charge PRO plus that allow the engine alternator to charge the 24v system while underway and charge all three while plugged in.

It is common to condense your marine electrical system down to two batteries.

  • Battery 1 is for the engine and all other 12v systems.
  • Battery 2 is connected in series with battery 1 (+ of 1 to – of 2) and the trolling motor 24v connection is made by connecting the negative to to Battery 1 (engine battery) and the positive to Battery 2.
  • You would be able to use your existing battery charge to charge both batteries, but the engine would only charge the starting battery while underway.

Hope this helps,


Conversion Aversion


My fishing boat wiring question concerns using an inverter to charge trolling motor batteries.

Can I plug my Guest Model 2611 battery charger into an inverter capable of producing at least 10 amps if the inverter is connected to the main motor (1994 Mercury 125 HP Optimax outboard) starting battery only while the main motor is running? Guest marine electrical battery charger

Thank you.


Hi Don,

This will work.

It is not the most efficient way to charge your boat’s trolling motor batteries while underway, but it is the most cost effective.



Thank you.

I am open to considering any other “more efficient” suggestions from you.

Please share your ideas.


Hi Don,

There are chargers like this one from Marinco that will charge all three batteries along with charging on the fly.

When charging the marine electrical system using the engine alternator, the DC charge is not converted to AC and then back to DC.

Hope this helps,


Switched Solar?


My marine electrical includes an Automatic Smart Battery Switch and was wondering how to install a trickle solar charger to it.

Should I bypass the switch, or should it be installed just like a Guest battery charger to the “house” battery? If so, do I still need a charge controller, and where should it be located (between battery and panel, or battery and smart battery switch)?solar panel

Thanks for all of your help.


Hi Greg,

In my opinion, the best location to connect a solar charger is to the house battery, but at the battery switch end of the boat battery cables.

Connect the positive lead of the charger to the battery switch stud with red cable from your house battery and connect the negative lead of the charger to the ground bus. Connecting the charger to the switch will help reduce the amount of clutter on the battery.

If you want the solar charger to charge the starting battery also, turn the switch to either ON (VSR will control the charge) or COMBINE (batteries are mechanically paralleled with the switch).

Hope this helps,