One Battery not charging

[capecodcruiser]

I have 3 batteries on my boat. When the engines are running, 2 of them are charging, the 3rd is not. I understand electrics pretty well, but trying to figure out which engine's alternator should be charging that battery. Any suggestions would be greatly appreciated. Thanks

 

[Nehalennia]

Are 2 of them on one side of the battery switch and 1 on the other?
Is your MBSS (main battery selector switch) on "ALL" when underway?
We'll need more info on your setup I think to help.

 

[tobnpr]

Neither alternator is going to charge that battery unless:
1) It is wired in paralled with one of the other batteries
2) It is connected to one of the alternators via a battery combiner, which allows charging of two batteries off a single alternator.

It is possible that the PO of your boat has it set up to charge only from the battery charger (assuming it's a three-bank charger).
Doing either of the above will allow you to charge from an alternator. If the third battery is for house loads, suggest you install the battery combiner to keep that battery isolated from your starting battery.

 

[capecodcruiser]

Thanks for the quick replies. I do have a selector switch and thought I had it set to "ALL", but I have to confirm. Let me do some more research tomorrow and maybe even a couple of pictures. All the wiring is concealed in the various tubes and shrouds so hard to actually trace a wire by sight. May have to get the continuity tester out. I did already find that they had 2 of the charge wires from the charger on that same battery and none on one of the others. So, at some point someone has already monkey'd with it. Unless someone knows a reason why you would have 2 on one battery.

 

[fc3]

Sea Ray installed an optional battery isolator that allowed one alternator to charge two battery banks or two alternators to charge either or both banks. Below is the one Sea Ray installed as part of the cross-over charging option aboard Just Ducky It's the gold anodized unit on the right.

It's a two battery, two alternator unit.

Help to know if your boat has a generator and if each battery is connected individually or if a set are connected in parallel.