The MTE P7 is a fine light when it works, but beside myself several have reported them dying. I'm sure it's just a bad connection and I'll be able to find and fix it, but you shouldn't have to. Your luck may be better.

IMO, you should have two headlights anyway if you plan to ride at night, and if you do, it's best to have two similar ones with the same batteries so you don't have to have twice as many spare batteries and twice the chargers, etc.

18650 cells seem pretty unbeatable.