I never tested the runtime on the Steelbeam lantern - ended up giving it to a family member. On a quick Web search, I'm seeing quotes of 16 hours of battery life for this one.

And here's another lantern that seems to be pretty popular on CPF (I haven't tried one):
Energizer 4D Folding Lantern
It's fluorescent, and supposed to get 40 hours of battery life if you turn on one fluorescent tube, 20 hours if you use both.