Charging while running is going to depend on the light... some will, some won't. My current Garmin UT800 will not.

As for the generic 18650 lights... I personally would avoid any of the ones with the spherical lens, or any of the really cheap ones.

That being said, I did use a NiteCore SRT7 for about a year and a half and found it to be a great light (used an SRT5 with a 14500 battery before that, but it was a little weak). It's not cheap, and it's a pretty tightly focused beam, so it works well on road at speed. One thing I specifically liked about the SRT series was that the output is infinitely adjustable between nearly nothing and full power. The downside is it's fairly heavy, so finding a good mount took a lot of trial and error. I finally settled on a mount off of ebay that allowed me to put it on a K-Edge style GoPro mount. The only reason I'm not still using it is because I wanted something smaller, lighter, rechargeable without removing the batteries, and had ANT+ connectivity to my Garmin.