Motorguide Onboard Charger?

I’ve just purchased a used boat with a Motorguide 3 bank on board charger, and am puzzled by how it functions. First bank is connected to my starting battery, which never requires further charging. Other two are hooked to my trolling motor batteries rigged for 24V system. When I plug it in to charge, or hit the test button to check battery charge,only bank one and two lights come on, bank 3 shows no activity. Is this happening because it is a 24V set up? Is only one bank charging both batteries, or is something wrong with the unit? I disconnected the batteries and hooked my old deep cycle charger to each one seperately, and both showed a full charge, so somehow the 3rd battery is getting charged. Is this normal?
John

I’m thinking that if it’s hooked up right it would show activity on all three banks even if fully charged. Sounds like only one bank is doing the trolling battery charging.

Just make sure the the three leads coming from the charger are clean, make solid contact, and are on right( pos. to pos., neg. to neg.). If this is all met, then you have a problem with the charger or a battery.
P.S. make sure the one lead is not hooked up on a 24v pattern to the two trolling batteries, and the other lead is hooked up to nothing, this would probably fry the unit. Each lead from the charger should be hooked up to an individual battery.
Hope this helps, and good luck.