Trolling motor loss of power

fish7777

Cadet
Joined
Jan 15, 2017
Messages
8
New member, first time poster.

I have an 82 pound Motor Guide Great White bow mount and also a 70 pound Minn Kota transom mount for the back of the boat. I have two Group 24 North Star deep cycle marine batteries, with separate 6-gauge wiring to each trolling motor.

The North Star batteries are one year old; the wiring is 10 years old and in good condition.

Everything has worked fine with trolling motor power until a few trips ago. The trolling motor starts out strong but loses power rapidly after a couple of hours of intermittent use. It happens with either of the two trolling motors.

When I got home today I checked each battery separately. Each battery was reading 12.6 V and 90% charge. I keep the trolling motor batteries always on charge using a Pro Mariner onboard charger.

Neither of the wiring breakers were popped.

Has anyone else experienced this or does anyone have any ideas of what could be causing these problems?

Thanks very much,

John
 

GA_Boater

Honorary Moderator Emeritus
Joined
May 24, 2011
Messages
49,038
Welcome aboard.

Clean all battery connections and plugs if any. Also check for corroded wiring.
 

gm280

Supreme Mariner
Joined
Jun 26, 2011
Messages
14,585
Very good suggestions provided above. It sure sounds like battery issues rather then trolling motors. And that is because you stated they start out running strong and then peter off shortly there after. So that points to batteries.

Trolling Motors usually don't get sluggish after running for a short period, but batteries surely do. So it is time to have the batteries tested as suggested above. Also, this is a great time to remove and thoroughly clean all the wire connections going from the batteries to the trolling motors. Corroded connections will cause such issues as well. The corrosion causes a resistive connection that when used starts to heat up reducing the current capabilities. You want every connection as bright shiny metal connections. JMHO
 

fish7777

Cadet
Joined
Jan 15, 2017
Messages
8
Thanks for the suggestions folks. I keep the boat in a garage and all the wiring and connections look perfect.

Considering each trolling motor is on a separate independent circuit, the batteries are the only thing in common. I splurged for the high dollar batteries because they have a 4-yr full replacement warranty and because they are a PAIN to get in and out of the boat (very hard to access, takes about an hour and comes with some busted knuckles). So I figured they'd last at least 4 years, hopefully longer.

Would a load test be able to diagnose these battery issues? I don't know much about load testing. However the batteries start out strong for a couple of hours, then go to less than half power. I wonder if a load test will show that?
 

ondarvr

Supreme Mariner
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Apr 6, 2005
Messages
11,527
Yes, a load test will most likely detect an issue with the batteries if there is one.
 

Marinescout

Petty Officer 3rd Class
Joined
Jan 1, 2017
Messages
81
I would have them load tested also. Are you near salt water? I'm from a wiring background and even though the connectors look good the inside of the wires inside the wrap could be corroded. If you have several strands of wire corroded your 6 ga just became 8 or 10 or 12. You get the point. The wires will not continue to run current they will get hot and cause a shut down much like having too small a wire to run an amp or similar piece of equipment i.e.: trolling motors. Salt water only makes it worse but fresh water will also..check your batteries first if they are good I bet it's the wiring or plugs/plug connector. So battery check then connectors then wiring. My local napa will load test batteries still in the boat so it may be worth a trip to your parts house and see if they can do the same may save you some headache
 

Marinescout

Petty Officer 3rd Class
Joined
Jan 1, 2017
Messages
81
Also if both motors are doing it see what they both have in common and check there. Kinda odd both batteries would go bad at same time I think
 

fish7777

Cadet
Joined
Jan 15, 2017
Messages
8
Thanks for all the help; I will definitely get the batteries load tested. FYI, I live 40 miles from the nearest salt water and have never taken the boat in salt water.
 

fish7777

Cadet
Joined
Jan 15, 2017
Messages
8
Update...

I took the batteries into the local battery shop where I purchased them. The batteries tested fine with the load test. The batteries weighed the same as new batteries, therefore I didn't cook them by overcharging.

However the batteries only had a 30 minute reserve time, which means the lower parts of the plates were sulfated. My guess is that a 2 bank 10 amp Pro Mariner charger won't work for North Star batteries.

The battery shop was able to bring the batteries back to a 160 minute reserve capacity by putting 200 A into each battery. They recommended buying a Dual Pro 15 amp 2 bank onboard charger, which I will do.

Thanks for everyone's help. I hope this update will help someone else.
 
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