A friend of mine tipped me off to these fans you are speaking of... at
Wal-Mart you'll find 2 or three different versions depending on which
department you're in - the brand is Ozark Trail in Camping and O2Cool
elsewhere. I've also seen them at Target and even my local supermarket. They
come in several different permutations of batteries stored in a hinged base,
batteries stored in the body of the fan itself, AC adapter included, AC
adapter not included. The prices are in the $10 - $14 range. On the box they
make a claim that the fan runs for 24 (24 or 27 or something like that)
hours on a single set of 8 D batteries. The operating voltage is 12V.

I got one with an AC adapter. I cut the "power brick" off and added a
cigarette lighter plug. The cord is about 6 feet long I'd say. I have a
cigarette lighter socket by the battery tray, so plugged in there I can hang
the fan in front of the side window. My wife & I camped out on a rather
warm, stuffy night and the fan made a huge difference - that little bit of
breeze was really nice. I was a little concerned about draining down the
battery, but I ran the fan continuously from about 10 PM to about 7 AM and
had no trouble starting.

Doug Fitz-Randolph
Freeport, ME