Their website says 3.0 - 9.0 volts, although I just got mine a couple of hours ago and the manual states 3.0-8.4 volts. Either way, it should be find with a 17670. I plan on running mine tonight with a 18650 ( 3.7-4.2 volts - same voltage as a 17670), I will let you know in a couple of hours...But I don't anticipate any problems...