Glenn, one BTU = one pound of water raised/lowered one degree. therefore, a
case of 24 bottles of 16 ounces each lowered 40 degrees takes 960 BTU's
removal. That is about 6 hours net effective running time for a standard
marine reefer using about 5 amps.

now, add in a couple of soda's, five pounds of fish, some hamburger, some
cheese, some milk, etc.

now freeze some of that. keep in mind that each pound of water lowered from 40
to 32 takes another 8 Bthu's, changing from 32 water to 32 ice takes 144 Btu's,
lowering from 32 ice to 10* ice takes another 22 Btu's.

keep in mind that 10* won't keep ice cream solid.