I realize there are plastic spacers to do this, but just wondering if this might work.
It would have to be loose enough that the o ring stayed in place on the battery and wasn’t pushed down when it was inserted.
No I sure don’t. I can’t recall when and and where I first heard that. It was many years ago, 25+ probably. I know I had overheard a friend saying it. In reference to what I am not clear.
I found suitable o-rings at the hardware store in a kit of various sizes. You know, the kind of thing displayed in the aisle for a couple of dollars, which you don’t need but you buy anyway because it may be useful some day. They are roughly 18mm inside and 25mm outside (so 3.5mm walls).
They grip the cell nicely, so they stay with the cell and don’t stick in the battery tube when the cell comes out. I use 2 per cell. I prefer them to the dedicated plastic tubes, which sometimes have sharp edges that can cut the cell wrap and don’t always stay with the cell.
I saw the idea in an advert by some flashlight manufacturer who included 2 suitable o-rings as the ‘18560 converter’.
The plastic tubes I posted above work good, they are well made (without sharp edges) and its plastic is somewhat flexible. They neither stick to the tube nor to the cell. They are commonly bundled with some (cheap) 26650 lights, or at least I got mine that way.
That’s a good idea.
Usually cells are oversize already so if you buy 18mm ID rings they will already fit tightly.
Then a 25 or 26mm OD will fit the flashlight tube, since the flashlight tubes are also oversized by several tenths of a mm.