I put a Dometic 40 on my powerboat. After its initial cool down, which takes about 45 minutes at a 2.5 amp draw (1.67 amp-hr) it runs for about 5 minutes an hour at 2.5 amps giving a total amp-hr consumption of approximately 6.5 amp-hours for the first day and then about 5 amp-hours per day after that. Of course, the system is only 40 quarts in volume, but it is enough for my needs.