Do 18650s rattle in 21700 lights?

Something i have been wondering, since i don’t currently have any 21700s if i buy some lights that use them and put my 18650s in them for now will they rattle/flicker?

18650 is shorter and thinner than a 21700. Without some tube or o rings it will definitely move around or probably won’t work at all.

18650 work fine in my Convoy S21A.

It will rattle because 18650 is smaller, use rubber ring to fill the gap.
Something like this.

I tried 18650 on several 21700 flashlights and it worked well because (in my case) they have springs on both ends.

Theoretically a 18650 battery is 3mm thinner and 5mm shorter than a 21700 battery. They certainly will rattle, and most likely won’t work without some type of spacers.

All of my 21700 lights work with 18650 flat tops. I use o-rings or a factory tube to center the cell. If you lights do not have springs on both ends, it is likely you will have issues with the shorter flat top cells.

I am considering the Convoy M21B and i have UR18650FM 18650s and some Samsung ICR18650-28As.
I have no idea if it comes with centering washers, though its not mentioned so i am leaning towards no.

Use factory tube and put a rubber band around it so it doesn’t slap up and down, or some electrical tape. Or even better just run a 21700, cells are cheap & the 21700 hold moer powa’s.

I do plan to get some but at the moment i don’t have any. And they are not easy to get in Canada, plus the current shortage.

I think you’ll find most lights that are 18650 and 21700 compatible may have a little bit of rattle to them when running 18650 cells, but they should be tested to ensure no breakage of circuit continuity. Besides, very easy to slip over a few O-rings on the 18650 to help with the centering.

Where do i get some?

Should be able to find some at your local hardware store or building center. 18mm inside diameter/ 21mm outside diameter. Walmart.com has listings for 10 packs for $5.49US. Not sure what access you have to that up in Canada (you are in Canada, right?). Amazon.CA probably has something close.

My fireflies 21700 adapters cause rattle, but you can just stuff some TP or something in there.

If anyone has some Canadian links or model numbers that would be nice, i don’t recall most washers having their inner and outer diameters stated.

I use a pair of O-Rings from a hardware store. I just looked a the packages and picked ones I thought would work. No rattles. And I like having sir space around the cell. As opposed to wrapping it in cardboard or something like that.
Length wise all seems to be an OK fit. Most of my 21700s are a tight fit length wise.
Seems like I used a magnet spacer in at least one of my lights - but I can’t remember which one(s).
All the Best,
Jeff

https://www.amazon.ca/s?k=o-ring+18mm+21mm&ref=nb_sb_noss

I don’t know how remote you are out there in Oh Canada, but if you’ve got a hardware store chain in reasonable distance, give ’em a call and see. Or, just pop over on eBay. You can get all kinds of cheap o-rings from China on the cheap.

I’ll check it out next time i get to the hardware store, don’t go there much becasue of covid but when i get there i shall look carefully. Probably ask a helpful associate.

I'm not a fan of trying to find things at hardware stores...

I would just do eBay or Amazon.

Search for:

o-ring 18mm 21mm

The shipping would cost too much.
I am surprised none of the lights come with spacers, most 26650 lights come with 18650 spacers.