Thanks, Pat, I might chime in later.Originally Posted by UNM1136
Thanks, Pat, I might chime in later.
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I may have overlooked the subject but, anyone have experience with Surefire rechargeable CR123's? I've been reading reviews on Amazon and some are saying batteries drain very quickly.
The rechargeables have (off the top of my head) about a third of the capacity of normal CR123's, so that would make sense.
IDPA SSP classification: Sharpshooter
F.A.S.T. classification: Intermediate
Couple caveats: I am usually only involved in large LI systems — hundreds, thousands, or tens of thousands of cells. The industries I serve are generally much more safety conscious than consumer and automotive environments, so it’s always possible for me to overreact. Finally, most of the systems I work with are rechargeable. I mess with primary cells but don’t live there professionally.
I use primary cells in all of my gear that doesn’t get discharged daily. Here are a few reasons why:
- Primary cells generally have much higher specific energy and energy density than secondary cells. I say generally rather than absolutely because within a given format more advanced examples of secondaries may be available versus primary, but I can’t think of an example.
- Primary cells are much less sensitive to
temperature than secondary cells. High temps will rapidly age secondaries (I won’t do the whole aging thing here, but a secondary that lives in your car is a particularly troublesome thing).
- Neither LI secondaries or lithium primaries have significant self-discharge. However, secondaries are often in circuit with stuff that has appreciable quiescent draw, and unless I have a good understanding of that for the appliance I’d rather not worry about it.
- most of my gear that could use a secondary uses cylindrical cells. Cylindrical cells
are hard to get with appreciable quality, where decent primaries are pretty easy to find.
I don’t run flashlights enough to get them over my secondary bar. If you all do, or you just like the idea better, here’s a little stuff about safety.
Here’s what’s dangerous about LI secondaries:
- puncture and crush. Not absolute, there are some that are not so bad, but commercially available cells are kind of a grab bag and are very subject to counterfeit. This is a problem for primaries too, though I can’t make a comparison.
- conditions which cause the lithium to fall out of solution and form dendrites which can pierce the separator and cause fires, to include:
a) excessive charge rates
b) charging after discharged below safe limits (let’s use 2.4v for NMC) — I noted a poster above getting danger close to this one
c) charging below 15 degrees C.
d) overcharge, charging above max voltage
e) discharging at too high a rate, normally as a function of resistive heating
you’ll note that most of this has to do with charging. It is not crazy to put most of the mitigating stuff in a charging system, for a small battery or single cell application with limited safety concerns. However, if dendrite formation occurs, it can make the cell vulnerable to thermal runaway which can then occur at a later time, whether the cell is in use or not. A secondary safety system that is not part of the charger can detect an unsafe condition and isolate the cell, which sometimes prevents TR.
If the system is built into the appliance, then so good. That’s why I use my laptop and phone and watch without much concern. All three of them can afford to have pretty sophisticated and well tested battery management systems, and are pre installed with cells of a reasonably known quality (pouch cells in all cases). It’s not an absolute - anyone can make a mistake. The cheaper, less certified, and less common (safety has an economy of scale too) the device, the less sanguine I might be about its safety. I don’t have a dedicated charger for 18650s handy and don’t know how good their systems typically are. If I had one, I would think carefully about its location and whether I thought unattended charging was a good idea.
I think ptc and cid devices were mentioned upstream. I would point out that many 18650s and 21700s don’t have those. They add resistance to the circuit and lower Reliabilty, particularly for high power devices. Don’t assume that the cells you’re buying have one, and don’t trust either the authenticity of a cell or reassurance from its distributor. Know your drugs, know your dosages.
it was also mentioned upstream that cell-mounted protection circuits decrease reliability. That is absolutely true. They also add safety. If we use the forum’s usual odds / stakes razor, is it worse if your light doesn’t work or if you have a 3’ jet of flame and molten aluminum pointed at your face? That’s a little extreme, but know your drugs, know your dosages.
it was also mentioned upstream that secondaries offer more power than primaries. This is generally true (contrary examples exist but they are very hard to come by). Remember that power for a cell is a function of its capacity — a 1Ah primary discharging at 0.5C has the same power output as an 0.5Ah secondary at 1C.
it brings up an interesting point about high discharge with devices designed to use multiple
Types of cells. What limits their discharge? Certainly nothing inherent about the cell. Have to think about that one.
Last edited by JAD; 09-05-2022 at 08:55 AM.
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