How long do folks reckon the fridge will runoff the leisure battery only without any charging input from either the engine or external electrical source?
2x80Ah batteries divided by 3,4 Amps of current when it is on gives about 47 hours of continuous freezing, in theory, and when nothing else is on.
Of course normally the compressor is operational only part of the time... 1/2, 1/3, 1/10th of the time, depending of the ambient temperature and the fridge load.
Regards
Andrzej