These are available in Walmart they make two models a 2 cell and a 3 4 cell 6 volt model. I tested the 6 volt model with NiMh batteries. The results are 2.278 volts .0002 amp there was a slight glow in the bulb. 4.16 volt .036 amp. 5.53 volt .077 amp. 6.92 volt the amps refused to settle down and went from .140 to .150 in 10 seconds. My guess is 5 cells is too much for this bulb. It might work with a 6.4 volt lead battery. Radioshack makes a nice one for lantern lights. With 4 cells and 40 lumens this works out to 94 lumens per watt.
I bought a 2 cell and gave it the same test as above. It produces a fair amount of light with 1 battery. The results are 1.4 volt .042 amp 2.8 volt .066 amp 4.2 volt went from .190 amp to .200 amp within 10 seconds. This bulb also cannot be run overvoltage without going into thermal runaway. I’m happy with both bulbs. They produce an even pattern that is not too bright to read a map at night. https://www.flickr.com/photos/63373992@N07/15971721236/ here is beam shots of the Rayovac 30 lumen on the left the Nite Ize 45 lumen in the center and an old Mini Mag 2 AA cell on the right. Yes It’s there completely washed out by the other two. The Rayovac is drawing .066 amp the Nite Ize is drawing .24 amp and the Mini Mag is drawing .59 amp.
The rayovac just survived 12 hours under water.
Also from Dorcydirect (and Sears)
That’s the 3v/2cell; they also have the higher voltage one.
its just an led and resistor.no surprise to me.