Minn kota 4 bank multiple red lights

[flipnstick91]

I have a 4 bank minn kota onboard, and it is showing 3 red lights(meaning 3 batteries are below 8v). Replaced all 30amp fuses on the leads. I have disconnected the leads to one of those batteries and hooked to a battery i know is good and the red light goes away. However, i tested all 3 "red light" batteries and only 1 is bad. Why would the charger show a red light for a battery that tests 12V? I should add that my mechanic allowed my batteries to die completely without charging them at his shop but now they will accept/hold a charge, just not from my minn kota. Could the bad battery have shorted out other banks in the charger? Red light batteries are cranking and 2 out of 3 TM batteries. Thanks in advance.