USB makes a ton of sense for me. I have three USB chargeable lights: Cygolite 350, Knog Boomer and a Blackburn Flea. The Flea charges the fastest, the Knog takes about 2 to 3 hours fully drained and the Cygolite will take about 6 or 7 fully drained. Honestly, all last as long as advertised and all charge within my shift for the ride home no problem. It makes sense for me since I commute daily, and have computers all around me (but not necessarily wall outlets). Truly, they are a godsend.

Did you follow the manufacturer instructions explicitly while charging the light for the first time? They often have a quirky regimen for the first charge to maximize battery life.

I don't think I'll ever buy a non-USB chargeable light again.