This parametric LiPo HardCase can easily be customized to fit your LiPo SoftPack and turn it into a proper HardPack. My design approach was driven by the following requirements:
1) slim design to fit many batteries and RC car's battery trays
2) easy to open to be able to clean out dirt and check the LiPo's condition
3) parametric design/size
4) no need for additional hardware (screws, threat inserts etc.)

As there is no "one fits all", this design allows you to easily customize the size to fit your individual LiPo battery size and cable position.

First step is to customize about the size. Don't use the slicer to scale the HardCase as this will likely cause the upper and lower shell to not fit together properly. Do it by adjusting the model parameters in Fusion 360 (load the file "Parametric LiPo Battery HardCase.f3d" file I uploaded, NOT the STL files). If you never done this before: It's really easy, just install Fusion 360, load the model and follow the 2 last screenshots in the picture gallery on this page. Use the parameters "Battery_Length" etc. to define your EXACT battery size. The parameters "Inner_Spacing_Length" etc. will add some extra margin around your battery and can be adjusted too. The given spacings/margins worked good for me.

Second step is to create individual hole(s) / cut-out(s) for your LiPo's cables. Based on your skills and liking, please consider one of these three options to do so:
1) Define the cut-outs in Fusion 360 (I found it easy to start a sketch on the battery and then extrude/cut through the shell)
2) Define the cut-outs in your slicer using the "add negative part" feature most slicers have
3) Print without cut-outs and create them manually after printing

Closing the HardCase is done by sliding a piece of filament into the small holes on each side. You might need to re-drill these holes after printing the parts. Best drill size is 1.8mm, but 2mm drills might work too.

If you're struggling to create a HardCase for your individual battery size, just leave a comment. I'll create the correct sized STLs for you and upload them here.