Minn Kota Precision Charger issue with new AGM Battery

[IMRedeemed]

Let me preface the following by saying I've read just about every post I can find on folks who've had similar (but not the same) issue w/ Minn Kota Precision Chargers over the years.

Have a 2017 Tracker Pro Team 175 TXW w/ 75 HP Mercury 4-stroke motor. I recently upgraded the Trolling Motor and Graphs. I also replaced the stock NOCO Genius on-board 2 bank charger with a new Minn Kota MK-345PC Precision Charger. Everything has worked great for months, while I had 3 Flooded Cell batteries (2 Group 27 for TM and original Group 24 for Cranking and Electronics.

Two days ago I swapped out my Group 24 battery for a new Duracell Ultra BCI Group 31M 12V 800CCA AGM Marine & RV Battery. Store confirmed and showed me battery was charged when I picked it up. I read thru the MK User Guide for the Charger and properly switched battery type to AGM. Unplugged charger and re-plugged in to confirm Battery Type was saved.

Charger went thru detection cycle and started charging on all 3 banks. TM Batteries (Flooded Cell) completed charge within minutes and lights turned Green. AGM battery bank stayed at 50% for over 2 hrs. I unplugged charger from wall and started again. Same thing. AGM bank never got past 50% after a couple of hours. I read in the User Guide that you could press the bank button once (during charge) to confirm battery type, which I tried. Surprisingly enough, after illuminating the AGM light, charger went to flashing Green on that bank, indicating battery was now charged.

Took boat out yesterday and fished for 1/2 a day. Plugged charger in upon my return. Pretty much the same thing happened. Flooded Cell TM batteries charged in about 2 hrs. AGM bank remained at 75% for a 5 more hours. Just for the heck of it, I again pressed the bank button and the charger detected it was set to AGM. Flashed yellow lights a second and again went to blinking Green (indicating battery was charged).

First thing this morning I called Minn Kota. Woman I spoke to had never heard of this issue. After my call, I unplugged the charger waited a few minutes and then plugged it back in. This time all 3 banks cycled thru detection, charge and then ultimately went flashing green (even the AGM bank). I decided to turn on my graphs for a few hours while I worked on some other things.

Plugged charger back in after running graphs about an hour or so. Flooded Cell batteries went to flashing green in just a few minutes. AGM bank was at 50% for a while and then 75% for the past 5 hrs. AGM bank just now went to flashing Green while I was typing this post.

Is this normal behavior? AGM batteries are not cheap and do NOT want to risk burning one up.

Charger is on a short 7 foot 12 gauge extension cord just to reach the wall.

[FrancoCialone]

I would call MK and let them know what's going on and ask for a new charger as well !

[CatFan]

With a big battery, it takes a long time to charge. Let it go for 24 hours at least.

[catdude28]

Probably nothing wrong with your charger. My PC charger takes much longer to charge the AGM as the wet batteries and has from day one. I have checked the voltage as it runs through cycles. Can charge the wet batteries in a few hours after fishing, but overnight to do the AGM. Do as Catfan suggested.

[EL Skeeter]

The deeper the state of charge on the AGM the longer it will take to charge.
My wet cells charge in about 1/2 the time of my Odessey 2150 st depending on Depth of Discharge of course.

[IMRedeemed]

Thank for all the help everyone! I think the charger is working; the AGM ultimately charges and I don't get any error lights. As several of you mentioned, it appears the AGM just takes longer to charge than the wet (flooded) cell type. This is contrary to what I had read and been told, but my experience matches what each of you have noted.

Thanks again!

[catdude28]

Thank for all the help everyone! I think the charger is working; the AGM ultimately charges and I don't get any error lights. As several of you mentioned, it appears the AGM just takes longer to charge than the wet (flooded) cell type. This is contrary to what I had read and been told, but my experience matches what each of you have noted.

Thanks again!

[OverTimeAgain]

I did the exact same thing when I bought a giant 31 X2 power agm.


My flooded leads charged in 2 hours, and the AGM takes like 12 hours!