My (Limited) Return to Flashlight Reviewing – Part II

Following on my Part I post, you may be wondering why I’ve decided to return to flashlight reviewing after a six-year hiatus.

I’ve lurked a little over the intervening years, to see what was new and emerging. A few innovations caught my eye, but nothing to really draw me back. In particular, emitter efficiency appears to have barely budged over the intervening years. Then I noticed how all the manufacturers had begun to produce 1×21700 lights.

So what’s so special about this battery class? The ICR chemistry is the same as standard 18650 cells – which had maxed out at ~3,400 mAh during my earlier reviewing years.  But the slight physical size increase from 18650 to 21700 means you can pack a lot more capacity in there – up to ~5,000 mAh, as it turns out.

Why is that significant?  Of course, extra capacity will translate into extra runtime when driving an emitter to the same level. But ~3,400 mAh is plenty of runtime for our very efficient emitters, even on their higher levels. No, the interesting point to me what was what this meant in terms of battery energy density – and thus how hard you can drive an emitter.

There are two main ways to increase the power density of a lithium-ion battery: improving the chemistry of the lithium battery itself (which of course would be hard to do with such a mature technology), or simply increase its physical size. Given the cylindrical shape of the cell, 21700 adds quite a bit more “oomph” over 18650 dimensions for a fairly nominal increase in overall battery/flashlight size. As an aside, you can apparently thank Tesla for this innovation – their early vehicles were based on existing 18650 cells, and they apparently convinced Samsung to build the 21700 class for higher energy density in their newer models.

There are two main limitations to how hard you can drive an emitter – how fast you can draw away heat (to prevent damage to emitter/circuitry), and how fast you are depleting the cell.  Back when I was reviewing, newer lithium ion battery chemistries (like IMR) would allow you to sustain higher discharge rates – but these cells had much lower energy density, translating into lower runtimes (and they typically lacked protection circuitry).

But 21700 hits a sweet spot with standard ICR chemistry in that its higher energy density means you can safely sustain higher discharge rates. So you can drive the emitter harder – at least for short periods of time, before thermal management mandates decreased drive levels. And you can still use standard protection circuits for safety.

To put things in context, back when I was reviewing lights, the compact 1×18650 class had pretty much topped out at ~1,100 max lumens with emitters of the day. But with 21700 cells and the latest emitters, you could easily drive the lights to 2,000, or 3,000, or even 4,000 lumens for brief periods of time. That’s a lot of output in something nearly as compact!

So here was this entirely new battery class that had taken over the field, and a whole new range of lights capable of super-high output. That certainly caught my attention.

But that wasn’t all – most major manufacturers were now bundling lights with branded 21700 batteries included. And these batteries featured built-in charging capabilities through ubiquitous USB-C port connectors (or, at a minimum, the lights had such features). So, stand-alone battery chargers were no longer required. Having gifted a lot of lights in my lifetime, needing to provide quality battery chargers (and training on how to use them safely) was always a very limiting (and costly) endeavour.

But now we have the conditions to produce the ultimate holy grail of every-day carry (EDC) flashlight technology – a reasonably compact light, with moonlight to multi-thousand lumen max output capabilities, all in an easily rechargeable fashion with no special gear required. One light that could serve as everything from your bedstand light to your outdoor search light to your glovebox emergency light. Hot damn, now we are on to something here!

As an aside, the use of bundled 21700 batteries is not necessarily a boon to all – while great for the general consumer, flashaholics are likely to find this a bit frustrating in practice. The reason is that due to the nature of very exacting tolerances when fully tightening the tailcap (since most lights have anodized threads), it’s possible that few (or no) other battery brands will fit and work in a given light. There is of course the general issue of whether or not there is an integrated charger on the battery (which makes them longer 70 mm), but also whether or not reverse polarity detection is used (and if so, how raised of a button is needed, etc.). The end result is that unlike the old days of 18650 lights – where most batteries would fit and work, once you clarified whether a button top was needed – a lot of the new 21700 lights effectively have a custom battery that can’t be easily swapped out.

In any case, my curiosity was piqued for this class. When I started looking at existing reviews, I was quickly frustrated to see relatively little in the way of direct comparative testing. Sure, there are many quality individual reviews out there of different models – but how easy is it to directly compare performance from existing reviews? Sadly, direct multi-light comparative testing seems to have fallen by the wayside in the years I was away.

So, here was a fantastic opportunity to comprehensively compare an entire new class of lights that have wide implications not just for the enthusiast community, but for everyday users as well.

I dusted off my old lightbox and ordered up a few compact 21700 models. I was able to recalibrate my lightbox for the higher output (see updated lightbox info here), giving me confidence that I could directly compare new 21700 lights to the old 18650 models. I then reached out to some of my old manufacturer contacts, many of whom were interested in sending me some specimens to test and review.

That testing is ongoing, and I will soon start posting my new reviews of 1×2700 here on

My reviewing format will be tweaked a little bit too. No, I won’t be producing glossy magazine photos of lights – just the basics to show you the build. But my data results and tables will now be more quickly and easily produced and shared. Indeed, even my entire new database will be made available in real-time (check out my How to Access the Database page to learn more).

And I’m also going to start adding a feature I always eschewed – a rating system for lights. Given my focus on this single class-level right now, I think it’s reasonable to finally start offering up an overall score, to allow you to quickly compare to other lights in that same class. If anything, my reviews are going to be more tightly data-focused, with less extraneous material (i.e., no more video overviews). But running my own review site will give me greater control and flexibility with the content – and you will able to post your own questions and comments right here.

What’s next after I work my way through the compact 1×21700 class lights?  I don’t know. I do plan to pick up additional lights here and there, in a curiosity-driven way. So expect to see the occasional higher-output thrower or flooder thrown in, maybe a keychain light or two. We’ll see.

I certainly won’t be returning to the volume of lights I used to test – that wasn’t sustainable. Let’s take things one light at a time for now, and see where this goes.

Be seeing you!




  • Some notes on batteries:
    No modern 18650 or 21700 cell uses an ICR (Lithium-Cobalt-Oxide positive electrode) chemistry (for cost and safety reasons), though I hear that smart phone batteries still do (ICR has the best volumetric energy density). This was already true with the classic Panasonic NCR18650B cells (3400 mAh).
    The easiest way to tell (manufacturers don’t like to talk about chemistry in their datasheets) is the discharge voltage curve: ICR cells are empty at 3.65 V, while more modern NMC and NCA chemistries are still about half full at that point. To visualize this, go to and compare the old-timey Sanyo 2600 mAh (red) with the Panasonic NCR18650B.
    While progress has slowed a lot, especially in terms of capacity growth, battery performance still did increase. As an example in cells optimized for the highest energy content, if you compare the old Panasonic NCR18650B with the newer Sanyo NCR18650GA cell, you will note a very relevant performance increase at medium to high discharge rates.

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