D-Cell to 18650 battery adapter

thingiverse

I tried out multiple adapters from D-Cell to 18650 but none of them worked for my quad D-Cell maglite. Such adapters allow you to use your trusty D-Cell Maglite in combination with more modern 18650 cells and the lately available P13.5 LED inserts for Maglites, like this one: https://de.aliexpress.com/item/32957921517.htm. Since 18650 cells are 65 mm long, you're somewhat limited in combinations. A 2 D-cell Maglite (= 12 cm length) would allow only one 18650 cell. A 3 D-cell Maglite (= 18 cm length) allows two 18650 cells in row ( = 13 cm length). A 4 D-cell Maglite (= 24 cm length) allows three 18650 cells in row. Each 18650 cell has a maximum cell voltage of 4.2 Volts. By using a LED insert for your Maglite with 3-18 Volts DC, you can power those with 1-3 18650 cells, while a 5-25 Volts DC insert requires at least two 18650 cells in row. You should consider using 18650 cells with integrated protection circuits only. Unprotected 18650 cells have spectacular short circuit current. I haven't tried out the D-Cell to 26650 adapter but it should work as well. The quad D-Cell adapter printed fine on my Ender 3 in vertical orientation. If you own one of those 6 D-Cell monsters, you might want to split the adapter in two halves and glue them together later. After printing out the adapter, heat up the end of the spring with a gas torch and bend the spiral to a smaller diameter matching the negative pole of the 18650 cells. Then remove the original spring in the end cap of your Maglite and get rid of the anodized black stuff at the inside of the screw cap. Some Dremel and a round grind stone or simply a wire brush for drills will do the job. I used 1.2x18x300 mm and cut the spring as needed for enough force. Springs are available very cheap from China and can be ordered via E-Bay.