Looking through the various prints that use a lithium 18650 cell in place of 2 D Cells, I ran across designs that required print support or parts I didn't have on hand. There was one that used aluminum foil which was intriguing but when I printed, it didn't work in my application so I ended up designing my own. I'd link this as a re-mix but I can no longer find the thing this is based off of.
No printing supports or rafts are required and heavy duty aluminum foil about 4 layers thick works well once folded into a 5/16 inch (8mm) wide and 3.5 (90 mm) long strip. I however use 8mm nickel strips that I have on-hand for spot welding lithium batteries. The nickel strips are better since they are more robust but a thicker strip of thicker aluminum would work similarly if you had a source. I suggest a strip from a frozen dinner but I don't think there are many that use aluminum containers. Maybe a pop can?
Please keep in mind that a single 18650 is about 0.7 volt higher than 2 D cells. So make sure your equipment can accept this before using.

In case you are wondering what I use that requires D cells, in the United States, simple gasoline (petrol) cans (plastic transfer tanks) now require a spring loaded valve to dispense fuel. This may work well for tiny engines such as mowers or leaf blowers but I use them almost exclusively for old tractors which hold many times the amount in a 6 gallon gas can . I now spill way more fuel than before and the long duration that I have to hold a gas can in mid-air cause ergonomic problems. To remedy this, I use a battery operated pump. Adding the danger of electricity and motors near gasoline and batteries to landfills. A less than ideal situation but I guess that is what governments are for.

Creality

Ender 3

No

No

10%

Slide a 3.5" strip of metal in the negative end of the print until the tabs at each end are about equal and bend the tabs flat (90 degrees). insert negative end of 18650 battery. Place into device requiring two D cell batteries.

This is a simple TinkerCAD design.