I've been using my VIS 500 for commuting in the city 80 min/day 3 or 4 days a week. I find I can reliably charge it once a week and use it all week easily, and sometimes well into the next week. I use the pulse mode, since I'm more concerned about being seen than seeing where I'm going. It's plenty bright at night, and it survives being dropped, rained on, and all the things you'd expect it to be subjected to riding around Chicago.
It's a great light - but even better is that when I messed up charging it, I got in touch with customer service and they replaced it. !!within 5 days!! No hassle, friendly service. I wish I needed a lot more bike lights!