I thought that the Heltec Wireless Paper Slim Case was the best case around for the Wireless Paper, but I wanted to power it by an 18650 battery. I modified the bottom part to add a space for the battery; this only replaces the bottom, get the rest of the files from that thing!

The idea is that you spot weld bent nickel strips onto each side of the battery, and the extra width of those strips holds the battery in place. Do not solder directly to the battery! Solder the nickel strips to your cables before you do the spot weld! And make sure that you understand how to safely spot weld to an 18650.

Print this upside down with supports. It could probably be modified by a real 3D designer to be support less, but I don't unfortunately have the experience to do so, this works for me :-)

As a bonus I've also included a version of the frame which has larger holes for screws to hold the wireless paper -- I've gone for 2mm diameter.