Well, unfortunatelly, Mastepiece pro-1 doesn't reach its full potential on 1x18650 or 3xAAA. You need at least 2xCR123, 2xRCR123 or 2x18650 (or equivalent in voltage). The circuit inside the head, has step-down converter, which needs bigger voltage, to run the LED at designed current. 1x18650 or...