My deep cycle battery is less than a year old and I ALWAYS put it on the charger as soon as i get back from a fishing trip. I use it to run a 12V 55 lb thrust bow mount trolling motor. The battery is at the rear of the boat and I have a 20' run of #8 wire to it.

Today, just a couple minutes after leaving the dock, I noticed on my depth finder the voltage was 11.9. I was currently using full power to get to my fishing location. The depth finder uses the same battery but is wired off a fuse panel fed by a different wire - I think I have about 8 feet of #10 feeding my electronics. Way overkill but I sometimes run a spotlight. So the voltage being displayed is the voltage available at the depth finder, not necessarily the result of the voltage drop across that 40' run of cable up to the front of the boat.

I guess I'm wondering if perhaps this suggests my battery is weak. It seems to charge fine. When I stopped the trolling motor the voltage went back up to something like 12.5, it just goes down to 11.9 or even 11.5 while the motor is actually running (after running it for awhile). I'm thinking that is getting kind of low and not giving me the power I should expect at the motor.  :-/

Nope! Its working fine. The motor is putting a huge draw on the battery relative to everything else you're using, and the decreased voltage is how the battery reacts to load. If it makes you feel any better I have a completely identical setup, 55lb motor, 20' cable and everything else on a seprate panel. Mine does the same thing.

I expect the motor to drop the voltage while it is running, just not that low. I think it is a sign the battery may have weakened. It is still under warranty (Walmart - but lets not have a brand depbate   ) and I know I can return it with no argument, I just don't want to do it if it is a normal condition.

It's perfectly normal and explained by ohms law.

As current increases, voltage decreases.  

Bad (loose, dirty) connections on the positive or negative battery terminals will give the same symptoms.  It wouldn't hurt to remove them, clean thoroughly with a wire brush and tighten.

Bad (loose, dirty) connections on the positive or negative battery terminals will give the same symptoms. It wouldn't hurt to remove them, clean thoroughly with a wire brush and tighten.

Ann-Marie is right, it wouldn't hurt.  After they are clean coat with a battery terminal grease to keep them from corroding so fast again.

Also what gauge wires are you running, Maybe the wires aren't thick enough (rated) to handle the amount of amps. touch them while in use, maybe there is a break somewhere in the line.

or simply check the connections like mentioned before.

memo

they are 6 gauge wire. the connections are all clean.

is it a maintenance free battery, if not check the fluid levels in the cells of the battery, if low refill with distilled water, unless extremely low then go to the auto store and get some battery acid.  Otherwise the drop isn't that drastic, check and see if the voltage comes up with a slower speed, if it does it is just the load of the trolling motor would be my guess.  You can also do a load test on the battery if it would make you feel better, but it all sound fairly benign to me.  You should put a ohms meter on your car battery and have someone crank it, you will see the same phenomena.

I am having an issue with my boat. I have a 55 edge Minnkota trolling motor on a 12-volt battery. The issue has just start where my trolling motor will run normal for and little but then during operation with foot on the button it will stop running and then come on for a couple seconds then back off.  If you don't use it for a couple minutes, then use it again it will function normal for a little bit... It does this at all speed setting... Then is you keep the button button pressed when it does the short bursts it will just continue the short bursts,,,, Last night it stops completely and had to let it sit for a few minutes before it would function again at all. This is driving me crazy. I have two used trolling motor of the same kind and both are doing the same thing. I have added another battery still the same thing. Need some guidance please. Has anyone seen this before???????

Do you have a circuit breaker at the battery for your TM? What kind is it? If it’s the cheaper not manually reset type then your circuit breaker is likely faulty and tripping prematurely then resetting when load is removed. Or you have a short somewhere in your motor causing an overload condition that is tripping the circuit breaker as it should. Start by temporarily removing the circuit breaker and testing or replace it then test. 
 
Photo is of the kind I’m describing. We used to carry a spare on our boat because of the failures happening often enough and causing exactly what you describe. Ideally if that’s what you’ve got replace it with a heavier duty manual trip/reset type. 

 

My trolling motor just stopped the other day crossing a cove.  It turned out to be the circuit breaker.  I put in a heavier one and have had no more trouble.

On 6/26/2025 at 9:44 AM, Bownarrows said:

I am having an issue with my boat. I have a 55 edge Minnkota trolling motor on a 12-volt battery. The issue has just start where my trolling motor will run normal for and little but then during operation with foot on the button it will stop running and then come on for a couple seconds then back off.  If you don't use it for a couple minutes, then use it again it will function normal for a little bit... It does this at all speed setting... Then is you keep the button button pressed when it does the short bursts it will just continue the short bursts,,,, Last night it stops completely and had to let it sit for a few minutes before it would function again at all. This is driving me crazy. I have two used trolling motor of the same kind and both are doing the same thing. I have added another battery still the same thing. Need some guidance please. Has anyone seen this before???????

 

The first part of your description sounds like a battery going bad.  When they age and you’re trying to draw more current than it can deliver it will go below the TM cutoff voltage.  The last description sounds like a circuit breaker that is getting hot and kicking off.  If you’ve tried a new battery and it does it then I’d look for the breaker.

On 1/12/2009 at 9:59 AM, wasabi_VA said:

they are 6 gauge wire. the connections are all clean.

20’ of 8 gage wire was your initial statement, 20’ of 6 gage wire will reduce DC voltage resistance. For you set up a 50 amp circuit marine breaker should work good.

Tom

Thanks, I was looking at the later post and then went to the first one, failed to notice the date

 

What the more current post sounds like is one of those gray, auto reset circuit breakers.  Might want to try one of these   Amazon.com: T Tocas 60A Amp Circuit Breaker with Manual Reset for Trolling Motor Fishing Boat Marine Automotive 12V - 72V DC Waterproof IP67 Protection | UL Certified : Automotive

 

Another cause I've run into on a TM doing this was a bad bayonet connection on the control board.  

I would recommend placing a voltmeter across the TM's battery power connector and see what it's doing.  If it's the circuit breaker, the battery voltage will be dropping out or way down.  If it's not dropping, then the problem has to do with something internal in the foot control, head or maybe brushes.

15 year old post guys. Ignore the first one and read the one from the necromancer.