Be aware that many high-power flashlights that take 21700 cells can pull a lot of amps, and since your cells are of questionable bulk origin, they might not be high-drain cells. It also varies whether flashlights take protected or unprotected cells.
this post was submitted on 13 Jul 2025
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There are many; the size has become very popular in the flashlight world. They range from $20ish budget options from Convoy to premium $100+ lights from Acebeam and Zebralight.
I maintain a recommendation guide that has some 21700 options, though that battery doesn't get its own section. For an inexpensive general-purpose light to buy several of, I like the Convoy S21E configured as linked. The Nichia B35A LED provides outstanding color quality with good efficiency.
This light isn't especially demanding electrically, so the concern another comment mentioned about pulling too many amps doesn't apply here.
Wow thank you for the detailed reply the guide and the specific recommendation this should help me find exactly what I need to start making use of at least some of these cells
I hope it helps. Feel free to post about your short list to get additional insights. If you're thinking about several lights for different purposes and you don't have a lot of flashlight experience, it may help to start with one low-cost option and think about what you'd like to be different in subsequent purchases.
I do notice that a lot of these flashlights reference protected versus unprotected cells but I'm not 100% sure what they mean by that here is a picture of the cells I have I don't know if those count as protected or not 
Those are unprotected flat tops (bare cells).
I have a wurkkos ts21 which is a fantastic all around flashlight that takes 21700 batteries and also works as a battery bank. There's the sofirn lt1s lantern which also allowed reverse charging. Anything from sofirn, wurrkos, or lumuintop is going to be high quality.
There's also some from Noctigon/Emisar.
For unprotected batteries, I like this site: https://18650-21700.com/
It’s been a while but I think it’s a two-person business. Unfortunately, my one experience buying from them was quite poor and I bought elsewhere. But the site has excellent info and seems to stay up to date on the best and latest batteries for high performance use cases.
One thing to note is that the site admin (Austin) focuses on rcs racing or something. It’s a different use case than flashlights and so I found that the judgements mixed into the information aren’t quite right. Still, the information is excellent and well presented. And it’s a simple place to find “the best” batteries currently available.
I have the molicel p50b’s. They’re excellent. Just be sure that you have a charger and flashlights that handle unprotected cells!
Convoy S21e