Beats me! USB chargers are low voltage low output chargers intended for small low capacity batteries. Small low capacity batteries can't run anything except a small low power light for any amount if time. Sone people are apparently OK with that - I'm not.

I want waterproof, high output and long runtimes. So currently I'm running multiple 10W high end P7 LED's from Vision X driven by 12V RC Lipo batteries. About the size of an iPhone and so far this week I've not yet charged it even using it during the daytime on the way in as well as in the evening on the way home.

One helmet mounted light is usually enough when the weathers good. But nothing seems to suck up light more than wet black asphalt. So when the weather gets messy - I'll add an addittional 4 element lightbar into the mix. May sound like overkill but light intensity varies with the square of the distance so to simply double the intensity at any given distance you actually need 4x the output. But those lightbar modules have shaped beams and may put out more effective illumination than an automotive headlight, but won't bother oncoming traffic when mounted low.