The datasheet for this battery holder mentions that it’s designed for use with protected 18650 cells. Can I still use unprotected 18650s in it, or would they be too short?
Hello andrei.alechin,
1865 indicates the physical dimension while the 0 digit indicates it is a cylinder cell. This should be a good fit, please review datasheet dimensions before ordering: Click here for datasheet drawing.
Protected 18650s tend to run a few mm longer than the name would indicate, by perhaps 2-5mm depending on the source. Scaled measurements from the drawing suggest the distance between the spring contacts for the P/N in question to be about 63mm, so an unprotected cell that conforms to nominal dimensions would probably make contact, though not be so well retained under spring pressure as one would want.
Thanks for the info 
I tried scaling some measurements myself from the dimensional drawings and got about the same. I suppose I could bend the spring contacts out to accomodate the shorted unprotected cell, but that feels like a bit of a bodge to me. Can you suggest an alternative that might fit an unprotected call better?
I’m not seeing much with that same 3-cell through-hole format on hand, though the 106990288 might be something to look at if you were planning for a series connection; the coil spring mechanism seems as if it may be a bit more forgiving dimensionally.
Yes, it would be for 3 cells in series. I’ll keep your suggestion in mind; at the moment I’m looking to see what will fit well in the enclosure I’ve chosen.