Facebook post that
@IkeInTexas put out ....
This is copied and pasted from Ian Wendt. Full credit goes to him.
This is in response to recently released high output LED lights having issues with certain batteries. It's a long post but worth your time.
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"So, I'm seeing that there seems to be a lot of confusion when it comes to 18650 batteries, the different kinds of 18650 batteries and how their performance differs, so let's go over it.
But first things first. Don't buy the cheapest battery you can find. It's just not a good idea. Cheap cells vary enormously in quality and performance and can be downright dangerous as they are often much more likely to catch fire during recharging.
So, don't be a cheapskate, spend a few dollars more for a good battery.
That out of the way, let's talk about current and current draw.
When it comes to flashlights, as lumen outputs rise, so does the current demand, how many amps the light requires to run at full power. Up to about 1000-1200 lumens or so, most decent CR123 batteries and all but the shittiest of 18650s will be able to keep up with the current demands without failing catastrophically (typically through over-heating and subsequent venting/explosion) or getting shut off by their built-in protection circuits.
The second you get up into 1400-1500+ lumen outputs, you're going to need more current than CR123s and standard discharge rate 18650s can deliver safely, Instead of, say 1.5 to 3 amps, you're gonna need cells that will deliver 5-10 amps or even higher with the really insane current demands from 20,000+ lumen lights.
As an example, I have a Klarus XT11GT that puts out around 2000 lumens, and it comes with an IMR battery (a special, more stable chemistry than standard lithium-ion) that is capable of a 12 amp constant current draw. The battery that comes with another Klarus, the 1600 lumen XT2CR, is a high-discharge lithium-ion, rated for 7 amps of constant current draw. I bring these up as examples of how different outputs and power demands should be paired with appropriate battery types.
If I were to put something like a Tenergy or Streamlight 2600mAh 18650 in either of those two lights, the likely outcome will be the lights not functioning at all, or if you're lucky, you'll get a few seconds or minutes before the protection circuits kick in and shut off the battery. If you're unlucky and also a cheapskate, the shitty Ultrafire battery you got for 5 dollars will have a faulty protection circuit, the current demand will overheat the cell and blow up the flashlight in your hand.
To summarize: Under 1200 lumens, discharge rate doesn't matter that much. Over 1400ish, it matters a whole hell of a lot. Don't buy batteries that don't have the discharge rate listed in their specs. (The one, notable exception to this is the Surefire 3400mAh 18650, and that's solely because I trust that Surefire tested them and they'll function reliably in their own 1500 lumen light.)
Capacity is next. Capacity is typically listed as mAh(Milli-Amp Hours) and the higher the number, the longer your battery will last before it needs recharging. 2600mAh used to be the standard, and you still see these around because now-a-days they're very cheap and easy to make. In comparison, a single CR123 is typically around 1400mAh.
For a few dollars more though, you can get up to 3600mAh batteries, which makes a pretty substantial difference in effective runtime. Again, don't be a cheapskate. 12 bucks buys you a Streamlight (Merh, American brand is best! Except the battery is made in China just like the others) 2600mAh battery with cells of unknown provenance, 4-6 dollars more gets you a Surefire, Nitecore, or Klarus battery, that uses cells made by Panasonic (largely considered the best quality cells on the market) and have 3400-3600mAh capacities. That's a hell of a lot more runtime for not a hell of a lot more dough. Did I mention don't be a cheapskate?
Chemistry. There's a few of them, but outside of specialist applications, the two you'll typically see in use in flashlights are lithium-ion and IMR. IMR will usually be somewhat lower in capacity although you can get them up to 3100mAh, and some of them can handle 30+ amps of current draw. Some of the really nutty high-output lights will ONLY function with IMR batteries.
Chargers. Don't be a cheapsk.... Skinflint. Buy a quality charger like one of the Nitecore or Klarus smart chargers. 20-30 bucks and you'll get something that will take good care of your batteries and your batteries will last longer.
Things not to do:
Don't buy unprotected batteries unless you actually know what the fuck you're doing and have an appropriate application. Used wrong, unprotected batteries can be exceedingly dangerous. Lithium fires are bad, mmmkay?
Probably stay away from flat-top batteries unless specifically called for in your application.
Other than Surefire, avoid battery brands that end in the word "-fire".
Don't buy just any old battery for your 1500+ lumen super-duper tactical light and expect it to work."
