A bit of a rough design for a charging box designed around the 3518 QC4.0 charging module.
The design could be done more elegantly but maybe someone will find it useful as it is. A design goal was to avoid having to use supports. I've added the F3D file as well so go ahead and improve it :)

The supply voltage can vary between 6 to 35 V. But in order to get maximum charging effect the voltage must be above 21 V.

The box has slots for inserting 8 modules. The slots are a tight fit in order to avoid the modules from sliding around too much when inserting USB cables.

I've added a fan to my box which I've hot-glued to the backplate because the modules get HOT(!) without it when charging with max effect. A On/Off cutout hole for a button has also been added. I'm using the button as a master switch to turn the box on or off.

The assembly process is;
1) Solder wires to the modules
2) Slide the modules in place.
3) Add (glue) the 'backstoppers' in the holes in the main box.
4) Fix wiring (modules/button/fan)
5) Glue the top lid in place.
6) Optional: Glue a fan to the backplate.
7) Glue the backplate in place.

The parts list:
1) 3518 QC4.0 Module
2) 10 x 15mm On/Off button
3) LM2596 step-down module for fan
4) A fan

Prusa

i3 MK3

No

No

I used polycarbonate as this is more temperature resistant. But I guess ordinary PLA can be used as well, as long as there is a fan installed.