1995 ProMariner 30 Battery Charger

Open the cover and look. Probably a third lead to the gen-set battery.

I would hate to think you have a loose "hot" wire hanging around.
So, Why are you changing out the charger?

My kind of boater.
Where do you need me sell and replace your charger.
USA is a little vague.

I'm not allowed north of the Mason-Dixon line any more.
Seems the highway cops have an issue with hardened Florida drivers.
Something about sings are a guideline vs some speed law.
Oh, something else about ammonia broadcasting on the side of the road.

So , keep YF up on your adventures on this and any other projects.
And, trace where that third red line goes.

What do the batteries serve that you are charging? Is there something else charging them while under load? Like engines, generators, etc? 5 amps is fine for float charging but I hope you have another charging source when the batteries are in use?

I don’t see where you ever mentioned what the battery banks are for? Are they just for engine starting or are these your house batteries? Or both? If they are house batteries you have lots of things they are servicing that are 12v. If this is your only charger you are going to have issues when on shore power and you only have this 5 amp charger to charge them.

Where do I start?

bilge pumps
Heads
Fresh water pump
Lights
Electronics

Yes some Of these will not be used when the boat is unattended but if you spend time on board at the dock, you will run your house bank down with only 5amp.

that is way to little charge.

In your first photo of your old charger it appears to be charging at about 8 amps. If that is your normal draw with the boat not in use your 5 amp charger is not enough. My boat has parasitic draw of about 7 amps (12v) just sitting there. Some of this is from my Fireboy system, alarm and monitoring, bilge pumps and float switches, etc.
if you look on your electric panels, anything on the DC side is battery powered. And then I’m sure you have more that is hard wired in. If you want to know for certain, just take a voltage reading of your batteries with a multi-meter. Come back a day or two after and see where it is then. If it’s lower you are not charging enough. Also, if your new charger is continually charging at full amps as shown on the LED indicator lights, you have too small of a charger.

What condition are your batteries in? The photo of your new installation shows one bank dead and the other bank low.

New does not mean good.

Also, You went from a 30 Amp to a (dual??) 5 amp. With minimal house loads, that 30 may have just been enough.
Usually Bulk, Absorb and Float are the 3 stages the newer chargers provide.
The Bulk pours some current into the battery to clear the sulfides. This is how the newer chargers help batteries last longer (or supposed to) vs just set to a float mode (final level).
IMO, those batteries will never reach a full charge.

I would consider your dual 5 amper a battery maintainer, like for batteries on a shelf during the winter.

Were not trying to beat you up, Just trying to help.