I tried this when a nice fellow CPF'er lent me his A2 and the Pila cell doesn't work. Pity since the lamp itself is designed to run off 3.6V. When I tested the PWM circuit, I scoped the voltage on a very nice Lecroy scope at work and it computed 3.6V RMS on the lamp. I don't completely understand why the circuit drops out well above that voltage. Maybe Surefire figures 2x123 is totally spent by the time the voltage is around 2V or so.
CM