Seems when I printed my 3rd pair of holders the positive end does not connect to the negative of the other battery. This worked fine for the first time using these batteries i the first two holders I made, but when I tested the third one they didn't. I even tried the first two again and now they don't work for them either. Most of the 18650 batteries I have do have little bits of the nickel connector that was spot welded to the batteries when they were part of the part of the laptop battery that I pulled them from. The ones I am testing with I managed to get all of that connector off them.
I do have a bunch of 18650 batteries I bought years ago that have the button caps on them and those work fine. As well as the batteries that still have the bits of the connectors stuck to them.
I do plan on having some type of washer of wire with a bit of solder on it t put between the batteries when I plan on adding a BMS to to them. That certainly will work for making that connection, but I was hoping not to have to rely on that.