The Blackburn 2'Fer gets the spec'd life per charge: 5 hours flashing, 1.5 hours steady (maybe a bit longer). But it's mainly a front or rear (white or red) warning light, bright and evenly diffused, visible from the sides, but not really concentrated enough to be a useful headlight. At $25 it's a pretty good value. I mostly clip it onto the front of my hat band, and have another flashing red LED on the back of my hat. With the bright flasher that way it really gets attention when I turn to look toward drivers pulling toward intersections and driveways. Lights up every reflective sign out to 100 yards. So far, so good, nobody has pulled out in front of me.

The Vivo-Bike Illuminati seems to get pretty good life per charge. I haven't measured it but have managed three one-hour rides between charges, and it hadn't exhausted yet. It's just bright enough to serve as a headlight, but I don't do much night riding. Good for $20 with the replaceable battery tail light, and there are others in that price range.

The 2'Fer and Illuminati are both USB rechargeables and include the USB cables. They'd probably work off my phone and Kindle tablet chargers too but I haven't tried 'em.

If I was riding at night more or commuting I'd look for something brighter with a battery pack to mount somewhere on the bike. And if I was choosing a new bike a hub dynamo would probably be on my priority list.