After reading this post by u/Paiolo_Stove, I ordered a couple of Vapcell 2015A batteries to test out. The comments on that post raised some concerns about protecting the battery and preventing short-circuiting. Yesterday, I received the batteries and opted to create a simple case using TPU, a rubbery plastic with exceptional layer adhesion.
To construct the case, the battery is placed into the print near the end (at layer 383 when using a 0.2mm layer height), and the print is then resumed, fully encasing the battery. The weight of the print is 6 grams, bringing the combined weight of the case and battery to just under 80 grams.
The source OpenSCAD file as well as an STL are available here: https://www.printables.com/model/407248-vapcell-2150a-case