We have a 2002 Islander 270, so don't know if the refrigerators are the same.
Our unit is a Norcold DC440. It is 12vdc only.
Holds 12 cans on top shelf, 12 on the lower shelf, and four in the door.
We bought the boat new in March 2002, and had it in dry storage until October 2002. It has been in the water ever since.
The refrigerator has been "ON" now for almost nine (9) years, running on the batteries/battery charger when in the slip on shore power, and the house battery when out of the slip.
The refrigerator has only been "OFF" when we are 'on the hard' for more than 24 hours, and that only happens every two or three years, when we clean, sand and paint the bottom.
Hope that helps.
Brian