I assume you're referring to cree/magicshine clones. I bought 3 of those headlights, all with batteries.

These are extremely bright lights, and the lights themselves are reliable. The batteries? Not so much. 2 of 3 work perfectly. The third stopped working, so I ripped off the protective tape and really all that's required is to re-solder one of two connections. Since I don't have a soldering iron (hadn't anticipated this repair after all), I just taped the wire back on with scotch tape.

It's working for now, but I'll obviously have to invest in a soldering iron to get it working perfectly again.

These lights and batteries are not covered by warranty as far as I can tell. You're stuck with whatever protection ebay and/or paypal offer, which may be a few months' of coverage or perhaps as little as a month.

Having said that, I paid a small fraction of the going price of $20-$25 per set (light/battery/charger). I probably paid $25 total for all three sets total.

I also bought a couple of flashlights. The on/off switches don't work perfectly. But the lights themselves seem to be reliable. I can assure you that drivers will notice these flashlights. I was 20 feet away from an intersection about to come to a stop. A car was doing a "california roll" through the stop light, UNTIL I looked in their direction, thus pointing the flashlight in their direction. The car came to a screeching halt, waiting for me to pass first.

I hedge my bets and always use both a helmet and handlebar mounted light just in case.