# 17670 vs. 18650



## was.lost.but.now.found (Jan 26, 2009)

I have been doing quite a bit of searching and can't seem to find a couple answers to some questions. I don't totally understand why these two batteries both exist when they are so close in size. Please help if you can - thanks in advance.

Would it be correct to say that in all cases 1 x 17670 will directly replace 2 x CR123 in LED lights (based purely on size compatability)?

Would it be correct to say that in some cases 1 x 18650 will replace 2 x CR123 in LED lights (based on space tolerances or boring out)?

If diameter is the only thing holding the 18650 back, then why didn't they make it a "18670" to get every little bit out of the space?

Are there any other considerations that need to be made when comparing compatibility?

Thanks for the help.


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## Kestrel (Jan 26, 2009)

was.lost.but.now.found said:


> Would it be correct to say that in all cases 1 x 17670 will directly replace 2 x CR123 in LED lights (based purely on size compatability)?
> 
> Would it be correct to say that in some cases 1 x 18650 will replace 2 x CR123 in LED lights (based on space tolerances or boring out)?
> 
> ...



Your first question, there a few older SureFire light bodies that take 2 CR123's but do not have enough ID to take 17mm cells. Not very common anymore. Those folks had to use 14 mm cells. It is generally accepted that all SF's can all take 17670's now (edit: at least I thought so, see below). Outside of SF it's probably the same thing, but that I'm not knowledgeable in that area. YMMV.
However, most have insufficient inner diameter to fit 18mm cells. Some flashlights and aftermarket bodies are made for this diameter cell though.
I don't really understand your '18670' question, 2 mm is within tolerances between brands, especially when protection circuits (which add length) are present / absent.


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## kramer5150 (Jan 26, 2009)

First of all, there are no generalized absolutes in this hobby, everything should be viewed and treated as case by case.

*I have been doing quite a bit of searching and can't seem to find a couple answers to some questions. I don't totally understand why these two batteries both exist when they are so close in size. Please help if you can - thanks in advance.*

They exist for other industries. Flashlight use is probably less than 1% of the annual production volumes for either, consumer laptop computers are probably the biggest industry drivers. Some laptops are big, with big screens and hence need higher capacity 18650 cells, others are small and can get by with smaller cells. 

*Would it be correct to say that in all cases 1 x 17670 will directly replace 2 x CR123 in LED lights (based purely on size compatability)?*

No... some of the smaller Surefire E series lights do not fit 17670 cells.... AFAIK.

*Would it be correct to say that in some cases 1 x 18650 will replace 2 x CR123 in LED lights (based on space tolerances or boring out)?*
Yes... in some cases but not guaranteed all.

*If diameter is the only thing holding the 18650 back, then why didn't they make it a "18670" to get every little bit out of the space?*
I speculate that the additional 2mm length is not worth the tooling investment for the fab house.

*Are there any other considerations that need to be made when comparing compatibility?*
Protected 18 and 17 diameter cells are slightly larger than that. They are also slightly longer. The extra layer of heat shrink and circuit board increases the overall size. If you are into DIY fabrication, make sure you tool up accordingly for the cell size. Its not often but sometimes you read about protected cells not fitting in commercial lights.

Avoid battery crusher types of designs. The springs should have sufficient clearance to avoid crushing the cells and protection PCBA.

Do not drop protected cells, you can damage the protection circuit.

_*Thanks for the help.*_
Sure NP


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## divine (Jan 26, 2009)

A CR123 is actually a 16340 cell, 16 mm diameter by 34 mm long. 1mm narrower than a 17*** cell. They will usually fit in CR123 lights.


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## 1dash1 (Jan 26, 2009)

was.lost.but.now.found said:


> I have been doing quite a bit of searching and can't seem to find a couple answers to some questions. I don't totally understand why these two batteries both exist when they are so close in size. Please help if you can - thanks in advance.
> 
> Would it be correct to say that in all cases 1 x 17670 will directly replace 2 x CR123 in LED lights (based purely on size compatability)?
> 
> ...


 
Based solely on size:

... No, just because a flashlight will fit 2x123 does not mean that it will fit a 17670.

... Yes, in some cases, a flashlight that fits 2x123 will fit an 18650.

... Because we, the flashlight community, make up a small part of the battery-consuming market. It is not cost-effective for battery manufacturers to cater to such a small segment of potential buyers.

... You've limited the subject discussion to size. So, as far as size is concerned, yes, there are other considerations - mainly length. Some cells are longer than others. Cells that are too long sometimes get crushed. Some flashlights won't operate properly if cells are out of tolerance. Still others operate intermittently (U.I. is affected). There's also shape considerations (primarily the positive terminal, some flashlights require cells that have a raised nub to make electrical contact).

_The only "rule of thumb", that I know of, is to follow the manufacturer's recommendations on cell type. If you want to substitute something else, then CPF provides a lot of archival information that may help you determine whether your substitution will work._


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## was.lost.but.now.found (Jan 27, 2009)

Thank you all for the great info. I do not have the capability (or desire) at this point to do any boring or other intensive work to make a battery conform to a space it does not want to go. So I'm making sure near future purchases all conform out of the box. I'm learning enough about voltage to know to buy only those that will fire up at a low enough voltage, but didn't fully understand other considerations like size restrictions. This helps a lot.


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