Here is my proposal for using the Nikon EN-EL1 camera accu pack as energy source for the Nikon Coollight SL1 instead of the very expensice CR2-lithium batteries.

Just shut the blank ends (coated with some solder) of the cable between the accu and the plastic cap.

 Connect  the other end to a jack - pay attention to the right diameter and - most important - that the insulation at the end of the jack is only 1 mm or less!

The accu pack can be fixed with rubber bands on the body of the Coollight or the camera.

Many thanks to K.-H. Drüsedau and Manfred Jensen who supported this modification :-)