E6 halogen has a sharp beam cut off, and if you make a 6v battery pack (5 x 1.2v) It will draw what it wants .
and so either 3w or 2.4w bulb will be fine..

As it is a common flange base bulb, a lot more than those 2 can be used ,
higher Voltage, match the Battery V available to Draw on.

Primary secondary pair are wired in Series ..