I had the larger Tecnautics unit which was engine driven--compressor and it worked well once the box was cold. I used the freezer unit and then had a spill over into the refrigerator box. I ran it twice a day for approximately 1 to 1 1/2 hrs and had no problem keeping things frozen. The key is to have a well insulated box, keep the freezer compartment full (I always started with frozen food and ice)and to limit the number of times you access the box. Randy at Tecnautics is very helpful and wants his units to be well thought of by cruisers.