Busch & Muller Ixon IQ lasts 5 hours on full power, carry a second set of 4 AA batteries and that'll get you 10 hours of great lighting, or go for the newer Ixon IQ Premium and get twice the light output on the same battery usage.
Around £45 from the German suppliers for the standard version or around £55 for the premium version, a bit more if you need the charger as well, but most folk have a AA charger already.
I use these, and the charger.
Allegedly the battery casing joint is a weak feature in the design, and the charger removes the need to open and close the case