I received my XP-G R5 SMini this week and have used it for both rides home. Total time: 1.5 hours and the battery was at 3.84 V. I hadn't noticed that it was overly dim. So it still had some time left on it. I used fully charged Callies Kustom 3100s in it. I agree that the form factor makes a great helmet light. It's a bit smaller in both length and diameter than my other helmet lights. If you want to go total ghetto, The Uniquefire 2100 XM-L is a good choice. See the reviews on budgetlightforums.com