A:  As outlined in the March issue of PY, using batteries to power onboard appliances continuously 24/7 contains a hidden cost—shortened battery life. Battery plates deteriorate as the current passes between them, so constant charging and discharging will speed the process.

Another consideration is whether your charger is the new “smart” sensing type or an older type that must be manually monitored and switched. Smart chargers monitor the state of charge in batteries and feed current to them at varying levels as needed. If the rated charging amps keep up with the draw, your system will work (keeping in mind the caveat above).
The old fixed rate of charge type is either on or off and must be monitored by a person to prevent boiling the batteries if it produces more power than the appliance draws. On the other hand, if it doesn’t, the batteries will run flat. We wouldn’t recommend it.

Most electric refrigerators have a built-in transformer that permits dual voltage. If yours doesn’t, the most direct route for you to get 12-volt power to your reefer is through a dedicated 12-volt transformer, as you suggest. This will reserve the batteries for times at anchor. They will last longer and you will still have chilled pop on hand for Friday afternoon getaways.
You will have to find out what amperage the fridge draws. This information is crucial to getting a transformer big enough to start and run the fridge compressor throughout its regular duty cycle. We recommend you consult a marine electrician.