If you need the light to run a long time at night then get a dynamo system, if you only need it for a short time but want a long battery run time then the Busch & Muller Ixon Core IQ is pretty good at 5 hours on high and 20 on low; and it runs on 4 AA batteries which means you could carry spare bats in your seat bag as long as the spare bats meet voltage and amp hour ratings of the original bats.