In my experience the run time on this unit (which I'm very happy with )@ 500 lumens probably 90 minutes or less, but frankly the useable brightness difference between the highest setting and the next one isn't that great, running the light on the high setting for the first hour and then switching to the next one down nets me 2+ hours of run time which is great. If that's an issue a second battery only costs $30 and it's easily pocketable so you can take it with you and swap batteries if you need more burn time. Great little light. I wear it on top of my helmet, I like it much better than any other lighting setup I've ever used. This time of year I ride in the pre-dawn darkness 4-5 days every week.