Using 2x CR123 in an 18650 light?

I noticed some JetBeams can use 18650's or 2x CR123's. Does this require special geometry in the battery compartment, or can 2x CR123's be used anywhere an 18650 is specified?

I've seen this to be the case with a lot of the mc-e and p7 lights as well that even if it doesn't specify it usually can take cr123's instead. How does this effect runtime and output too?

No, 2 CR123s can not be used ANYWHERE an 18650 is specified, and an 18650 can not always be used where 2xCR123s are specified.

For example:
Jetbeam sells models designed for both 2xCR123s OR 1x18650, physically either combination is the same length (very close anyways), so they will fit fine, however, jetbeam ALSO sells versions that are 18650 specific, they have a regulator optimized for the lower voltage input of the 18650 as compared to a pair of CR123s. If you were to put 2 CR123s into one of these, you would fry the electronics.

Always check manufacture recommendations, or, if in doubt, do a search here and check through stickied threads to find safe combinations that work in various flashlights.

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Keep in mind that an 18650 is nearly 2mm thicker than a CR123, so they will generally only fit in lights designated for use with them.

I was afraid you were going to say that. The problem is, I don't want to invest in expensive rechargeable lithium batteries and the associated equipment if I can avoid it, because I'm already up to three battery types I use for my electronics (AA, AAA, and CR123) and I don't relish the idea of making my battery collection that much more expansive -- especially when the only thing I'll probably ever have that'll use 18650's is a flashlight. I never even heard of them before I came here.

Wow. Thanks for the primer. All I ever wanted to know about batteries.

Actually, 18650 batteries are the cells that are used in laptop batteries. If you have an unused laptop battery laying around, chances are that it has upwards of 8 18650 batteries in it. They are not protected and might not be any good, so you have to be careful.

I found that investing in 18650 batteries is worth it in the end. You can get 2 decent trustfire batteries for about 10 bucks, and a charger for around the same. If you make sure the voltages are ok, then cheaper chargers and batteries can be ok. You then get more runtime (a lot of the time) than 2 cr123 lights, and you don't have to pay $3 for every few hours of light runtime. In my opinion, 18650's are way more cost effective than cr123's.

I wasn't aware they were used in laptop batteries, but that's good to know. I doubt I'll find any other use for the individual cells, though, and I've already invested close to $500 in CR123 lights. The CR123's are definitely pricey, but I can use them singly or in pairs, which means they fit all of my lights that don't take AAAs. I like that kind of interchangeability. Not to mention, when the asteroid hits and civilization crumbles, I can raid the local supermarket to stock up.

Along that line of thought, the Jetbeam Jet-3 M looks pretty nice, what with the continuously-adjustable brightness and all. But I'm kinda hooked on the cute little lights for right now. Maybe I'll save that one for later.

Do I already know you, Mjolnir?

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EDIT: How often do 18650's need to be replaced? A few dozen cycles? A few hundred?

deusexaethera said:

... and I've already invested close to $500 in CR123 lights. The CR123's are definitely pricey,.....

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$500 would have been enough to setup a very nice solar recharging station for end-of-times type stuff

Not to mention, when the asteroid hits and civilization crumbles, I can raid the local supermarket to stock up.

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Most locally carried CR123s are priced ~$3-8 per cell...

EDIT: How often do 18650's need to be replaced? A few dozen cycles? A few hundred?

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Usually a few hundred, depending on how they are used and stored. Keep "extra" cells in a cool place at ~50% charge (check em every few months) and they are ready to be charged up and run good for several years thereafter. Having a stock of CR123s on hand and some lights that are compatible is never a bad ideas, since these primary cells are generally good for at least 10 years in storage (or better)...

Eric

To add on, 18650 cells are 3.7 volts (or 4.2 volts fresh off the charger) while 2 x CR123s will be either 6 volts (primaries) or 8.4 volts (fresh RCR123s) and if your light is not designed to accept 8.4 volts, the additional voltage might fry your light or drastically reduce the lifespan of the LED.

EDIT: The Jet III Pro ST (bugoutgear says that its discontinued, thank goodness i already own one) specs say that its max voltage is 4.2 volts so if you chuck in 2 x CR123s or 2 x RCR 123s, you will damage the light IMHO

deusexaethera said:

Along that line of thought, the Jetbeam Jet-3 M looks pretty nice, what with the continuously-adjustable brightness and all. But I'm kinda hooked on the cute little lights for right now. Maybe I'll save that one for later.

EDIT: How often do 18650's need to be replaced? A few dozen cycles? A few hundred?

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The Jet III M will run on 2 X Cr123.
The life of 18650's varies with the quality of the battery and the quality of your charger, it will also depend on how they are treated. I have cheap Chinese 18650s that are at least a couple of years old, I have also had a couple of batteries that have died prematurely.
Norm

mdocod said:

$500 would have been enough to setup a very nice solar recharging station for end-of-times type stuff

Most locally carried CR123s are priced ~$3-8 per cell...

Click to expand...

Ah, but when the asteroid hits and civilization crumbles, there won't be any sun -- the sky will be full of dust! That's why we'll need all these damned flashlights!

(besides, I would just steal the batteries if I had to. )

I do see your point, though; but it wasn't my call for the little flashlights I got to be designed to use CR123's. I do wish there were at least one other thing I could use the 18650's in; that would make it a lot easier to justify buying them.