Do you still remember? That one thing you absolutely had to have as a teenager? For me, that was a Maglite with large D-cells. Not just any flashlight, but that specific one. A massive and heavy club made of aluminum that felt like it could survive a nuclear strike and whose light beam you could focus. It was the epitome of adventure and reliability.
Recently, while cleaning up, this exact lamp fell back into my hands – my old Maglite 4D. A wide grin spread across my face, followed by a slight sense of disillusionment. The four huge and heavy D-cells were long gone, and the original light bulb was little more than a warm tea light compared to today’s LEDs. Throw it away? Never! Instead, a new project was born: An upgrade for the 21st century!
MagLite 4D to 18650 adapter and cells
The Mission: From 4 Lame Donkeys to 3 Racehorses
The solution lies in the voltage. After I replaced the original 6V bulb, which was still working, with a modern LED bulb with a wide voltage range of 6-24 volts, the path was clear for modernization. Three 18650 batteries connected in series provide a nominal voltage of 11.1 volts – perfect for the new LED and a huge increase in runtime!
The Solution: A Custom-Made Adapter from the 3D Printer
The special features of my design:
- The Main Adapter: It securely holds the three 18650 cells. To bridge the contact from the positive pole of the foremost battery to the lamp head, a piece of 1.5mm cross-section copper wire is simply bent into an elongated U-shape and threaded through the two designated holes.
- The Flexible Negative Pole Cap: At the end of the adapter, there is a small, separate cap I designed, through which another piece of copper wire is threaded. This completes the circuit to the spring in the Maglite’s tail cap. You can also use a piece of aluminum foil pressed into the right shape here.
- Built-in “Play”: Not all 18650 batteries are the same length. Protected cells are often longer than 65 mm. No problem! If your cells are a bit longer, simply omit the negative pole cap and replace it with a small, crumpled piece of aluminum foil. This gains you the crucial millimeters, and it will always fit.
MagLite 4D to 18650 adapter
MagLite 4D to 18650 adapter cap
The Bulbs!
When selecting a bulb, the base type is important. There are three different types of bulbs (P13.5S, BA9S, and E10), and you need to check which type is installed in your flashlight.
MagLite 4D to 18650 Adapter Leuchtmittel
I had a P13.5S bulb installed, so I bought an LED bulb from China like the following one.
Get the print files for your own Maglite conversion project!
Maglite 4D to 3x 18650 Battery Adapter
It’s an incredibly satisfying feeling to not only preserve such an iconic piece of technology from one’s youth but to make it better than ever with a bit of creativity and modern technology. The old, sturdy aluminum lamp finally has the power it deserves after so many years in the basement.
Happy building!
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