3 volts. they told me the rechargable batteries are usually 3.7 volts and can zap the LED.
be VERY careful with CR123 3v rated XRE LED lights... some will not handle 3.7v RCR123 (fully charged - some get to 4.1v). I learned the hard way - zapped one of my 3v only Cree Q5's... not only will a 3v only driver get zapped, it may, on rare occasion, catch on fire with the wrong batt.