This is an adapter to use 18650 batteries in place of most any tube style batteries.The included OpenScad script has support for D cells and C cells in the script. Simply uncomment which ever battery type you have, and comment out the other. The length of the tube is based on the num_cells value.

If you need to create a holder with a different outer diameter, add a new block containing your desired values, as so;

cell_diameter=XX;
cell_length=YY;

Be sure to comment out any other cell_XX blocks.

I built this in order to upgrade my very old Maglite that used 3D cells and an incandescent bulb. I replaced the bulb with an LED upgrade that works from 4~24 volts. I got the LED bulb and the battery clips off Amazon.

I've included STLs for 2~7 D-cell and 2~7 C cell.

You can create a tube to use some other cell types by modifying the battery_diameter variable.