but I’d just like to know what y’all expect impedance of new cells to be to give me a better idea of how degraded my used cells could be based on their IR values.
18650 cell impedance/IR is manufacturer, part number, and chemistry specific. There are basically 2 different type of chemistries. ICR and INR. There are also hybrids of both chemistries.
INR/NMC are usually your high drain capable cells with a lower IR range ≈10mΩ to ≈35mΩ.
ICR/LCO are usually your low drain capable cells with a higher IR range ≈35mΩ to ≈80mΩ
Your hybrids will fall into any of those ranges but generally are "mid range" ≈25mΩ to ≈60mΩ
The best way to determine the SOH "State of health" of a specific make - model cell is through experimentation. Taking an IR reading when harvested, charging the cell and running a capacity test. I have done that to 6000+ cells, download/view spreadsheet
here, and have come up with a "cheat sheet" you can download/ view
here. This by no means is an authoritative document, but it is my findings on IR values that produce acceptable capacity results by cell manufacturer and part numbers. Unfortunately there is no magic single mΩ reading that encompasses all 18650 or any Li-Ion cell format. It is learned by taking the manufacturers "spec" with a large grain of salt and adjusting the mΩ readings to your findings. You will find though that "most" ICR laptop batteries that are any good will be in the ≈<60mΩ range. The difference between a good cell (considering a cell with 80% SOH as good), a marginal cell and a bad cell can be just ±5mΩ. There are some stragglers like the LG*(*)S31865(0) that will perform well up to 80mΩ but for sake or IR consistency for a battery build I would not use them.
Wolf