parallel 18650 battery holder

designed to be used in parallel, but can be wired in series if you ignore the polarity indicator.  
Use 8mm nickel strips cut to 50mm lengths to form the contacts.  Bent in half, insert from top down through the two slots and bend inward or outward depending on your application needs.

There is a small button to assure a tight fit with your battery.  Depending on the dimensional accuracy of your printer, there is a small hemisphere in the center that can be shaved down to allow additional room.  

additional items used:

nickel plated steel strip.  cut to 50mm long pieces

https://www.amazon.com/dp/B08RHP8NDD?psc=1&ref=ppx_yo2ov_dt_b_product_details