onboard battery charger gone bad?

my trolling motor is slowing down like the batteries are not fully charged. When I plug in the 2 bank onboard charger the lights that show charge don't light up at all on one bank and the other shows one light blinking red. When the batteries were fully charged a couple of months ago, it would light up one light green. I hooked up a regular battery charger and it shows that they are NOT fully charged. I bought the batteries 3 months ago but they are not marine batteries. Is this my batteries or the onboard charger? The onboard charger is 8 years old.

Check all your connections and check water level in batteries if you can.

if they are not marine batteries that is more likely the problem, regular auto batteries DO NOT like to be discharged and recharged like deep cycles do. read this.


What is a Starting battery?
Starting batteries (sometimes called SLI, for starting, lighting, ignition) are commonly used to start and run engines. Engine starters need a very large starting current for a very short time. Starting batteries have a large number of thin plates for maximum surface area. The plates are composed of a Lead "sponge", similar in appearance to a very fine foam sponge. This gives a very large surface area, but if deep cycled, this sponge will quickly be consumed and fall to the bottom of the cells. Automotive batteries will generally fail after 30-150 deep cycles if deep cycled, while they may last for thousands of cycles in normal starting use (2-5% discharge).

What is a Deep Cycle Battery?
Deep cycle batteries are designed to be discharged down as much as 80% time after time, and have much thicker plates that a standard automotive battery.

What is a marine battery?
Marine batteries are considered a "hybrid" battery which actually fall between the starting and deep-cycle batteries. Marine batteries are usually rated using "MCA" or Marine cranking amps which is rated 32 degrees F, while CCA is at zero degree F. (For more information on CCA, CA & MCA, please see below)