When I got my convoy I also ordered the tube for 18350 cells but it took me until now to find one. It seems they are a very hard cell to get and only one vape shop around had any. It’s a great size and easily fits in any pocket, perfect EDC size. My convoy has 4-7135 cells so on high it draws about 1.4amps. I was hoping to do a runtime test on high but with the small tube it heats up far too fast to properly test without fear of overheating. I was using it on medium for over an hour and never noticed any dimming. I dont know how useful the really powerful lights are with this battery since it heats up incredibly fast but for medium output it’s quite usable. I see a lot of custom S2+ triples with this cell but I can see that heating up even quicker so I’m unsure how useful it is. 18350 seems most suitable for small lights while still able to put out decent current but vapers are moving away from them which means they will be getting harder to buy sadly.
I use the Bestfire cells I got at Gearbest a few years ago when they had a sale. Paid only 1.50 per cell before points.
The cells are nothing to write home about, but they are OK cells. works in triples.
But yeah, wish there were more cheap, reliable and good 18350 cells.
Plus the shipping costs these days….
Far as I see with my research we dont have any other readily available small cells that can give us the performance like these. I guess 14500 is the only other common one that would make sense. I know I could order some good ones online but don’t feel like spending over $20 for one battery
I looked into 18500s after seeing a S2+ pill/thread mod on here. But those cells are also pricey.
Since about a year we have a new type of 18350 cell that has both better performance and higher capacity. Those are great for these flashlights. At the moment there are two brands that sell them, Vapcell and Keeppower. The links are examples of where to get them, with some searching you can find them cheaper. And I see that you are in Canada, if I recall well it is quite hard to buy Li-ion batteries over there.
I might’ve been the one to point out that about 18500s.
Swap the reflector for a TIR lens (shorter), and with the shorty tube you can squeeze in an 18500 in place of the 18350, which’d sometimes make intermittent contact with the spring if you rap it.
Extra length in the battery makes up for the shorter lens. It’s a tighter squeeze as far as the springs are concerned, but nothing traumatic.
I did that mod a few years ago. Replace the reflector for a triple TIR. Shorten the pill a bit and you can easily get enough room for an 18500.
However, nowadays this mod no longer makes sense. The problem is the best 18350s are now better than the best 18500s except in very low powered lights (Vapcell recently released a 2000 mAh 18500, but unlike the new 18350s their new 18500 isn’t suitable for high-current).
Aliya’s Battery Store and Lucky Electronics Store on AliExpress both sell Keeppower 18350 cells, and are among the (few) stores recommended around here that will ship to Canada.
But since your typical usage seems to be pretty low-drain, you may not see a lot of benefit shelling out for more expensive cells.
Adding to those 2 brands , the Keeppower 1100/1200mAh are also good.
I bought these not too long ago…
Just ordered 10x KingWei 18350 1000mAh PostNL shipped. Will make them undergo a set of capacity and DC internal resistance tests. Intuition tells me they're the same high capacity and discharge cells others are asking some more money for (see BestFire IMR18350 1500mAh review @ lygte-info.dk). 
