Without knowing what load the fridge is drawing...hardly worth a guess.
Plus if the fridge is in a poorly ventilated space...it is keeping itself warmer than the rest of the boat... Granted we would hope the fridge is better insulated than the compartment so its a small difference..but still...my fridge cycles quite often and need help on several levels.
So without a amperage draw number...even a decent guess...hard to say.
Would the fridge have a low voltage cutoff? Mine doesn't as the PO had a non-marine compressor put in a few years back, but don't some have one?