We have an old (read 25 years) Koolatron we bought when our kids were little. It has served us well for all those years. It's similar to this one:
http://www.compactappliance.com/xq/J...roduct/P75.htm We never got the A/C adapter but just ran it off a battery charger since it had two little knobs for hooking it up to a battery. The bad thing is if you hook it up backwards it heats instead of cooling. Have to really watch the plug-in and color coding on the little knobs. My daughter borrowed it once to keep things frozen and ended up thawing it all. They've probably made that better by now. What we liked about it was that it's all electronic except for the fan - no refrigerant, it uses technology developed for the space program. I don't know what the others use - i.e. Coleman, etc. We always packed the frozen stuff up by the cooling fins and it would stay frozen for a week or more. The other stuff we didn't want frozen we'd put toward the other end and it wouldn't freeze unless we turned the dial all the way down. We have run it on the TV battery over night and didn't run the battery down - unlike the refrigerator in the TM! Good luck in your search!