Will I be glad when we get past the age of Li-ion batteries and their tendency to fail, swell up, and catch fire. Luckily instead of paying for another crappy replacement, someone had a 3D model of the case, which uses the easier to source (and replaceable, but still Li-ion) 18650.

Model on Thingiverse:

https://www.thingiverse.com/thing:3523791

My build, with photos of the electrical contacts:

https://www.thingiverse.com/make:992596