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MK 4 Bank on Board Charger

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Good Afternoon All,

I have a 4 bank on board charger (about 3 years old or so). It has worked flawlessly so far. Well I had a battery go out (so I thought) a few months ago, got a new battery and things were fine for a few trips. Well now when I plug the boat in to charge the batteries, battery #2 will show charging at 25%...when I come back some hours later it still shows charging at 25%. If I leave it charging I come back and the green and red light are solid with no yellow charging light. I did that a few times and still nothing. So I just took that battery back thinking it was too dead to charge and when they tested it they said it was reading reverse polarity. They gave me a new battery and I just installed it (everything is hooked up correctly (red to red, black to black lol). When I plugged it in it was showing charging at 25%, which caught my attention as it should have come with more of a charge than that but anyway, I just looked again (about 2 hours) and all my other batteries are charged almost full but that one still says 25% yellow charging. I am afraid it is going to go back to green and red here in the next few hours or so just like it did on the other battery. Any suggestions? Is my charger causing reverse polarity to the battery??

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I have a three-bank MK 345PC that had problems recognizing and charging all three batteries. I read on a forum, somewhere, that Minn Kota’s Precision Chargers are unusually sensitive to inadequate line voltage.


Yeap, I didn’t really believe this, either. However, I bought the heaviest gauge extension cord of the shortest length necessary to connect the charger to the wall socket. It worked, for the most part, although I still sometimes have to unplug the charger and plug it back in before it will properly recognize and charge all three batteries. Luckily, that happens only very rarely, now.


If you have flooded lead-acid batteries, another potential issue is poor equalization between the cells within the battery, although that’s unlikely, since your batteries are new. The charger has an Equalization Mode to fix that:




Finally, you should make sure there is no active draw on the batteries when you plug in the charger. The user manual indicates this is a potential problem.

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If I ever bought another charger it would be a Dual Pro. Had one for about 8 years and it was amazing. Charged batteries that were in poor condition for years. I have had a Minn Kota for a year now and no problems however. 


When I bought my Dual Pro I read a lot of reviews and the only charger with no bad reviews was the Dual Pro. 

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This is a very easy problem to diagnose. Take the leads from one of the other 3 known good ones and put it on the new battery. If the battery charges without issues, you have an issue bank /w that leads on battery 2 that won't charge. If it throws up the same error, you have crap luck with batteries and need another. You should have a multimeter if you own a boat. If you don't, get one. Check the voltage on your new battery /w nothing connected to it. Clean all your connections spot clean, too.  Gauging your battery voltage by what the charger says is like relying on your GPS for correct voltage. Use your multimeter for an accurate reading. No idea how the warranty on the MK chargers work or if you can repair a single bank on an MK. I use dual pro's. 


RED and GREEN lights are lit simultaneously for each bank if any of the following apply:
A) A short circuit.
B) The battery voltage is below 8.0 volts.
C) A damaged temperature sensor on the output lead. The bank will stay in maintenance mode if this

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