Amps don't mean anything without knowing Volts. When you're talking battery charging
and chargers you need to separate the Amps going into the batteries (at nominally 12 Volts DC) from the Amps being used by the charger
(at nominally 120 Volts AC).
The battery charger
you linked to puts out 1.25A @ 12 Volts DC (nominal). That's not enough to do anything other than keep the batteries topped up and prevent self-discharge if they are already fully charged. See the link from the website below, for a battery of any size it indicates their "chargers" are for "maintenance only".
The Freedom, on the other hand, is
intended to charge your batteries when they are deeply drained. If you use it in power sharing mode then not as quickly as full-out, but at least far more than 1.25A. In power sharing mode the Freedom uses 5A @ 120 Volts AC (again, nominal). If the Freedom was 100% efficient at taking your AC from the generator
and converting it to DC for your batteries you would be able to get 50A @ 12 Volts DC. (And how we get there takes way more than a crash course).
That's all theory. First, your generator
probably puts out a little less than 120V AC. Then, your batteries probably need a little more than 12 Volts to charge (like 13.8-14.4). Then there is resistance everywhere, and finally, your Freedom isn't 100% efficient, but more like 80-90% efficient. All in, your Freedom (set for 5A) should be delivering something like 35-40A into 12 Volt DC batteries (assuming they are in a state of significant discharge).
In your posts several back said the AC voltage from the generator was dropping to 80 Volts? That sounds like you have too much load on the generator, even with the Freedom set for 5A. I would recommend turning off every other AC load on the boat. Make sure that includes the fans, the water
heater, everything. Leave on only the Freedom. If that all works then you can add other devices one at a time and see what brings up the load and trips the breaker. I'm suspecting a heater of some sort, but not knowing any of the details of your setup it's a shot in the dark.
Maybe you could post your battery sizes and a list of your AC devices?