I don't like the common mold 18650 battery case. Mostly they are not suitable for the flat end, without protected board version battery, I mean the positive pad cannot contact the battery which waste a lot of my assemble and debugging time.  I draw this one with fusion 360. and add 2 holes to tie the string to remove the battery easily. The metal contact is from the toy AA battery contact pads.

You can see how it works on my tweeter. 

[https://twitter.com/i/status/1414981333810565121](https://twitter.com/i/status/1414981333810565121)

Material I used on the video is wood filament PLA.