We have one that we take on long road trips that will actually freeze
bottles of tea (not so much my Pepsi, since it's under pressure). I've seen
it get as low as -4C, with the temperature inside the car around 70-75. It
does, admittedly, force a lot of air past a pretty large pair of Peltier
junctions (it draws enough current that I've had to repair the internal DC
power connection once, and the accessory cigar-lighter socket in the car
once.) It's not a really large cooler, about .4 cubic meter or less, so
there's a good ratio for cooling. Biggest hassle I have with it is if the
lid is not tightly sealed, the panel inside the cooler that contacts the
Peltier (to transfer the cooling) will frost up and it gets very inefficient
in a hurry.