Re: Battery charger repair
First thing I would do is contact Minn Kota directly, either by phone or email. I've done that in the past and they are very responsive. Here's a link to their contact page:
Minn Kota Motors
I got interested because I had a problem with a Minn Kota portable a few years back and I conversed with them via email got good response, although no real resolution other than, "I guess it's broke." I googled my charger and the 3rd result was my post at iboats 9 years go titled MKC-10 Won't Shut Off.
MKC10l My problem was the opposite of yours - the battery got charged but the Charge Complete light wouldn't come on.
I found the manual for your charger which included a dis-assembly schematic. There's really not very much too it, btu there is one item shown as item 6,
BOARD. I'd bet that is where your problem is and maybe Minn Kota can hep you with it. Good luck.