Replacement Battery Charger / Power Station

Go for a Progressive Dynamcs
If the coverter is stand alone or you wish to keep current one as a "Back up" 9200 line If the converter is attached to the power distribution box. 4600

Buy an inverter/charger, this prepares you for the day you decide to add solar panels.

I would go with a stand alone as the previous poster suggested. I bought the 40 amp B&D charger and it does a good job on 2 6 v GC batteries. It has an equalize function at 15+ volts and a desulfating function. I don’t think any of the newer “smart chargers” completely charge your batteries. I use my onboard constant charger to complete the charge and to maintain the batteries. If you don’t have more than 1 or 2 batteries it is a cost effective way of charging and maintaining your batteries. How long did you charge your batteries when you read 12.1 v? Even old or inexpensive charger / converters will charge your batteries if they are good.

Charge for 168 hours.
Add solar.

You can change the converter,
or,
you can get a stand alone charger to connect to the batteries directly.
The built in converters, WFCO etc are not great, most on here seem to prefer the Progressive Dynamics and others for when their WFCO unit fails, but instead of changing out the unit you can use a secondary charger.
Just depends on time, effort, money, convenience and which is higher on the decision priorities for you.
One advantage to consider though for the standalone charger is that many have the "Boost" or jumpstart feature which is also useful for your tow vehicle as well as giving you a charger for other purposes.

Also if you are adding solar, that may become your higher voltage charging method.