18650 to D-Cell Adapters
thingiverse
These adapters allow the use of a single 18650 lithium-ion cell in place of two alkaline D-Cells batteries. Once printed, simply string suitable copper wire through the slots to act as contacts. I recommend solid 10 gauge wire as is used for most household electrical circuits. EDIT: This latest version should be much easier to wire, and I feel silly for not thinking of the slots instead of the holes until today.
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