Maglite 4D to 3x 18650 Battery Adapter

Turn your childhood dream, the classic Maglite 4D, into a modern high-power LED flashlight!

This 3D-printed adapter allows you to replace the four heavy and expensive D-cells with three powerful, rechargeable 18650 Li-ion batteries. Breathe new life into your old, rugged aluminum beast and make it brighter than ever before.

IMPORTANT: What You Need (Please Read!)

1. LED Upgrade (Mandatory!): This conversion outputs approx. 11.1V. The original 6V incandescent bulb will burn out instantly. You need an LED bulb rated for a wide voltage range (e.g., 6-24V).
2. Check Your Bulb Type: Maglite used different sockets. Before buying an LED, check if you need a P13.5S, BA9S, or E10 type bulb.
3. Copper Wire: You will need a short piece of copper wire (approx. 1.5mm² or 14-16 AWG) for the electrical contacts.

Assembly

1. Print the main adapter and the optional negative-pole cap.
2. Bend a piece of copper wire into an elongated U-shape and thread it through the two holes of the main adapter. This bridges the contact to the positive terminal of the battery.
3. Thread another short piece of wire through the negative-pole cap.
4. Insert your three 18650 batteries and close the assembly with the cap.
5. Tip for Longer Batteries (e.g., "Protected" Cells > 65mm) If your batteries are a bit too long, simply omit the printed negative-pole cap and use a small, folded piece of aluminum foil as a contact to the spring in the tail cap. This gives you the flexibility you need!

Full Story and Project Details

You can find the full story behind this project, more pictures, and details in my comprehensive blog post (English and German language):

https://www.blogyourearth.com/top-story/maglite-4d-wie-mein-kindheitstraum-zur-modernen-led-leuchte-mit-18650-akkus-wurde/15619