Surefire has never recommended using the Lux V KL4 with three CR123 batteries. They have recommended using the KL5 Lux V, also utilizing a constant current boost circuit, with three CR123's, something that has always puzzled many CPF'ers, particularly those that have good knowledge about constant current boost circuits. Many have surmised that a Lux V LED with a high vf (forward voltage) would be able to tolerate being over driven at 9 volts, and the voltage sag of the CR123's would soon drop the voltage down below the vf of the LED, and then the KL5 would run in regulation. Also there is more metal in the KL5 head to draw off heat from an overdriven KL5 boost circuit. This premise for the the KL5 would not work with the KL4 because there is not anywhere near the mass of metal that the KL5 has, and we know that the KL4 gets hot fast at standard specs with two CR123's, or one Li-Ion.
Bill