Sunday, October 14, 2018

The Adventures of SiG in 18650 Land - Part 1

I'm just envisioning a lot of  people saying "what?"

The generic term 18650 refers to a battery that has become very popular in the last couple of years.  The leading 18 refers to the cell diameter and 65 refers to its length, both in millimeters.  I have no idea what the trailing 0 is supposed to mean.  They're quite a bit bigger than the familiar AA battery, and those dimensions show the 18650 to be very similar in size to what's referred to as 4/3A at 17x67 or 4/3 Fat A at 18x67.  (There are literally about 85 standard sizes for batteries other than AAA, AA, C and D cells).

There may be an exception, but every 18650 cell I've seen is a Lithium Ion battery and most tend to be higher current capacity than a AA rechargeable.  The picture gets more complicated from here.  I'll pick that topic up in few minutes.

If you have a tactical flashlight like a Streamlight, Ultrafire or some other brands, you may know about these batteries because they have become very widely used.  Likewise, they'll get used without your direct knowledge in things like the power banks available for charging your phone on the go.  For example, one like this, which based on its ratings and size, is probably a single 18650 cell with the required circuitry.  I believe they're at the heart of things like car jump starters I've talked about before, but their use in laptop battery packs is probably where industry first cranked up to make lots of these batteries. 

I started down this road into 18650 land because of a battery powered light I found while looking for something else.  Not a flashlight, it's a bike headlight leftover from the days when the only time I could ride my bike this time of year was after dark.  (It's long since obsoleted by the manufacturer, but it resembles this one).  I found this light and a pair of batteries, long since forgotten.  Due to their shapes, I'll call them the bottle and the brick.  Both were Nickel Metal Hydride batteries, NiMH; the bottle measured more like 5 cells (over 7V open circuit after 16hours on a trickle charger) while the brick measured more like 4 cells (over 5-1/2V).   I believe the brick was the battery I used with this headlight while riding.

You would probably think it would be remarkable if they worked after years in storage.  I did, too.  After several discharge/recharge cycles, it turned out that the bottle would run the headlight for a while, while the brick wouldn't.  Neither was "good", but the bottle was better.  It's capacity curve looked very reasonable when supplying 1 amp, for over 2 hours.  When I say it's not "good", it's not like a new battery and can't be charged faster than a trickle rate for 16 hours.

I had started to think that it would be nice to have this bright light available in the aftermath of a storm, or any other blackout.  Lights are always good.  After some effort, I was able to measure the current the headlight drew, which allowed me to size how big a battery pack I would need: it would have to be over 4V and rated one amp*hour for every hour I wanted it to run it at max brightness.  As a test, I ran the headlight for over two hours on maximum brightness from a pack of 4 AA NiMH Eneloop Pros that I borrowed from a handheld radio, just as my "1AH per hour" predicts.  That meant I knew I could just buy another pack of those, but I got interested in the capacity of the Li-Ion batteries.

A quick search of Amazon and eBay showed a bewildering assortment of 18650s.  Worse than bewildering, I would say a preposterous assortment.  One the one hand, you have reputable  companies like Samsung selling a 2500 mAH rated battery - identical to the smaller AA Eneloop batteries I tested - while on the other hand you'll find companies you've never heard of selling batteries rated almost four times that capacity.   I'm not a battery designer, but I understand what goes into them and how they work.  While it's true that in a given sized battery, current can be increased somewhat by increasing the surface area of the electrodes, the capacity in mAH depends most on the battery size.  As a result, I honestly don't believe anyone on earth can get 9800 mAH out of any 18650-sized battery, if the companies with a good reputation are claiming 2500 mAH. 

Worse than ridiculous claims for batteries, the marketplace is also full of outright fraud, counterfeit batteries and counterfeit components.   After some looking around, I found a site dedicated to a niche use, home made battery packs for home made electric bikes.  That site ended up having lots of good solid information, including this gem:
Here is a video of disassembling an 18650 shell that has a very tiny 4.2V battery inside. Counterfeits are everywhere these days!

If you begin shopping for loose individual 18650 cells, and you find advertisements for 4200-mAh cells that put out 30A per cell…they are lying (Trustfire, Ultrafire, etc). An authentic Ultrafire cell is not horrible, but again, there are lots of counterfeits.

Buy some samples of the cell you think you want to use. Set-up a current-drain pulling the same watts that the cell is rated for, and…if it is too hot to hold in your hand after 5 minutes, its a fake. It may even look exactly like an authentic Samsung, Panasonic, or LG cell. Once you find a trusted vendor, only buy cells from them.
Using this guide, I narrowed my search to a few part numbers, eventually settling on Panasonic batteries rated for 10A surges and 3200 mAH, then found a seller on eBay with a decent package at a good price

More adventures in 18650 land will follow.


  1. I first stumbled on these batteries when I bought a couple of UltraFire LED flashlights on the basis of a recommendation from one of the blogs on my sidebar.

    They're also used for the big "vaping" devices some people use, and they pack a pretty big punch. One charge lasts me considerably longer than 3 high-quality CR-123 batteries in one of my "tactical" LED flashlights, and they pump out more light, too.

  2. I'd stay away from any eBay 18650 seller, SiG.

    Hit up r/flashlight for some good suggestions.

  3. I haven't played with the Lithium batteries, but I suspect you can look for fakes, and high output versions, by the weight. That was one of the factors to judge Nicad cells. If they were lighter, they wouldn't have much reserve power. It was real common with Horror Fright battery tools. Pick up an 18v battery pack, and it would feel empty. Open it up and it looked ok, as the cells were proper sized, but they didn't have much content, apparently.

  4. I'm wondering if the same trick that works for Nicad would work on your Li batts? Use a DC voltage source a bit higher than the batt or cell and momentarily touch the contacts. On my 18v tool batts, I dialed up my tig/stick welder to about 24 volts and zapped them. Brought about 50% of dead ones back to life. I have a vague recollection that some batts grow whiskers across the internal parts, shorting out the cell. Shocking them blows the whiskers apart. Probably work better if I did each cell directly. Next batch.

  5. From what I understand, quite a few rechargeable tool batteries (drill/drivers, for example) are made with 18650 packs. The better ones (Dewalt, Milwaukie, etc.) using better quality 18650s. Poor ones (like several Craftsman tools I bought) have light-weight 18650s in the pack, with low Ah ratings. The tools were fine, but the battery packs _and_ the chargers failed quickly.

    I learned my lesson with Ultrafires. All have been lightweight compared to other 18650s, some ridiculously light, as if they were merely a shell. I didn't open them, but I started buying Samsung and Panasonic 18650s and staying away from most of the rest. I have bought some good batteries with the Nitecore brand on them (for my Nitecore and Olight flashlights and headlamps), some of them with high discharge rates which power 3600 lumen and 9000 lumen flashlights.

    1. It's true you can tell a good battery from the bad by the weight, and most of us have a reloading powder scale or something to weigh them, but it's hard to get the weight of a battery being sold online, or in a store if it's packaged.

  6. Don't buy batteries from Amazon either, that source has been poisoned with counterfeit batteries from sellers who use Amazon's co-mingled inventory to hide their fakes.

    There are a few good sellers in the US and some semi-trusted sellers in China, but the shipping of Li-Ions from China has changed and now costs more, making the price not as good as it was just a few years ago. and are a couple sellers of batteries and chargers trusted by r/flashlight and BLF (


    The current highest capacity for an 18650 is around 3500mAh.

    If you want capacity with a lower max amperage - Samsung INR18650-35E 3500mAh (13A), LG 18650 MJ1 3500mAh (10A), Sanyo/Panasonic NCR18650GA 3500mAh (10A)

    If you need a high amperage, but with a lower capacity - Sony US18650VTC6 3000mAh (30-80A), Samsung INR18650-30Q 3000mAh (15-20A), LG 18650 HG2 3000mAh (20A)

    LiitoKala, Nitecore, Xtar, and Opus chargers are most often recommended.


    Latest "Arbitrary list of popular lights"

    Here is some more info on dodgy batteries.

    And a good comparison of most of the available 18650 batteries.
    And the reviews

    Charger reviews

    1. Thanks for the links, Ratus. I've just barely started scratching the surface on this, and haven't seen any of those.

      It is drinking from the firehose!

      Likewise, I came to the same conclusion about Amazon. I'm sure there are good sellers there, but there's no reason to think an Amazon seller is any better than a guy at the Flea Market. Don't even know if you only picked the Amazon Choice, or Sponsored if it matters. I came to the conclusion they were worthless after looking at a half dozen listings or so. User reviews were worthless. There was one review on one battery with a guy saying he measured the capacity and the batteries were good. Everyone else only talked about being able to vape again, or that it fit their flashlight.

    2. Let me know if you want anything else from the flashlight side.

    3. Ratus, you beat me to sharing those links, Mountain Electronics is the first place I'll send anyone looking for lithium cells and chargers. I've bought a lot of cells direct from China, but it's a bit of a gamble and and you need to know how to tell if you lost.


    4. Hey, Joat. How have you been?

      I'm doing drivers now, TA 17mm and 21mm regular or e-switch, your choice of firmwares. Hit me up if you want any.

      My last cells direct from China were the eight 35Es with my BLF GT and a couple of 18350s with my group buy of the mini GT. The only reason was I knew they'd be genuine and the price good.

  7. Ah, the wonderful world of batteries... and of battery peddlers.
    I've got several maybe-next-year projects queued up in the back of my head, requiring various sorts of battery packs, from "maybe I could get away with using a bargain-basement giant model airplane pack" to "definitely need a large LiFePO4 pack with serious battery management", by way of "hey, AGM batteries are looking pretty cheap, aren't they?"
    And, yes, those popular-size cells seem like they ought to be a good idea, what with economies of scale and all, if only the supply chain were trustworthy.
    Looks like you've got some informative comments already; I'll likely return eventually, seeking further enlightenment. (Or enmotorment, according to what I'm trying to power.)

  8. I've heard that the 0 at the end of 18650 means it's a cylindrical cell.

    1. The profile of the cell seen end-on? I’m only partly kidding, but it’s as good as anything I’ve heard.

    2. I heard that a long time ago, but totally unconfirmed by anyone it the flashlight community.

      It's probably like how a 2032 coin cell is 20mm x 3.2mm, 18650 are 18mm x 65.0mm.


      Also here is a link to the, slightly out of date, flashlight wiki.

      Most of the general info is still good, but the list of manufacturers and light suggestions are way out of date.