I have a light which I run 4 “aa” eneloops I made years back. It was a driver made for 18650 voltages but it tolerates the initial 4.8v of the eneloops - if it were alkaline aa it would be closer to 6v too much I think.
I used a princeton tec battery headlamp battery carrier for the batteries and made the rest out of copper pipe and old flashlight pieces.
I still use it all the time. Changed out the head band and the TIR lens