Here you go. Try these. Let me know if they help. They are error free.

triple 18650 v3.obj
triple 18650 v3.STL

As for free software, Blender is probably the most powerful but has a steep learning curve. Still, it's really great. There is a CAD program called FreeCAD I think that will do solid modeling. Finally, try Meshmixer. It's a slicer too.