# Best rechargeable replacement for 2 CR123A cells



## Stainless (Jan 29, 2006)

I am (finally) trying to get into using rechargeable batteries. I have some rechargeable AA cells from my digital camera - no problem.

I want to use rechargeable cells in my Luxeon lights that use 2 lithium CR123As. What is best: using 2 RCR123As, which might come off the charger at different voltages, or use a single 18650? The voltage levels confuse me - the little cells are listed at 3.6v - 4.2v EACH (total of 7.2v - 8.4v), and the longer cells are listed as 3.6 volts - and I only need one?

I just need a place to start - I do not need the absolute "best" solution.
Any recomendations as to what to get and where to get it?

TIA


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## FredM (Jan 30, 2006)

What lights do you have? My L4 surefire runs great off of a single Pila at 3.6 volts cause of the regulation.


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## nerdgineer (Jan 30, 2006)

I don't use rechargeable Li-ions so this is based on general principles and not any experience. I think you first have to check the diameter of your light to figure out what can fit into it. Some protected RC123's are too wide or too long to fit into a light. Ditto with the 18650's (protected or not). It would be good if regular CR123's rattled a little in your light. 

A really tight light might be limited to 17650's or unprotected RCR123's only. This would mean slightly less capacity (with the 17650's) and/or the possibility of reverse charging one of your RCR123's in use.

If they fit, the best solution by the numbers seems to be the 3.0 volt RC123 rechargeables sold by AW to avoid overdriving your light and reverse charging a battery by accident.

Some lights ae specifically designed for 18650s or 2xCR123's (like Dae's or AW's) so they would be fine with those, but otherwise there is a risk of overdriving with 2xRCR123's or underdriving with one of the longer Li-ions. I don't know a way to find out except to experiment or look around for someone else's experimental results.

Good luck.


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## Stainless (Jan 30, 2006)

The first light that I want to outfit is a Vital Gear FB2, with 3w led module.
I think I will check out what AW has to offer. At least I know that I am not completely crazy to believe that this is not a simple pursuit.

Another question: When I read about batteries having unusually high voltages "hot off the charger", does that refer to temperature in the literal sense? If I let them cool down to room temp before using them, will they have lower/safer voltage output?

Thanks.


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## Lunarmodule (Jan 31, 2006)

Stainless,

The phrase hot off the charger refers to the peak charge voltage the cells have when removed from the charger and the cells are still warm from the charging process. It really was coined to reflect NiMH and Nicd cells to drop considerably in voltage especially in the first several hours after charging. Some of my NiMHs for example show 1.55V/cell off the charger, drop to 1.43V in an hour, and 1.35V after 24 hours. When using incandescent lamps that have a tendency to "instaflash" or burn up the filament from too much battery voltage, it became common practice to "rest" cells overnight and allow the voltage to drop before using them in an incan light to minimize the risk of that happening. 

Lithium ion rechargeables are totally different animals, they lose almost no voltage after charging and do not have a linear relationship between open circuit cell voltages and percentage of charge remaining like NiMHs. They also have very little self discharge, I've had lights in storage for backup use for months read 4.15V when they came off the charger at 4.19V. 

The main point is this: there is a significant voltage difference in rechargeable 123s and other sizes in that the chemistry provides 3.7V nominal under a load but almost always start between 4.1-4.2V when fully charged. This is a big concern in 2 CR123 cell lights which are really 6 volt designs. For many of these lights, a 17670 cell is an exact replacement for 2 CR123 cells, although the voltage is lower. However, rechargeable LiIon have a very low internal resistance and deliver current more easily and with less voltage sag than primary (disposable) cells, so for a lot of lights a single cell the length of 2 CR123 can work well, sometimes underdriving the light a bit. Some LED modules have a degree of regulation to them that allows for a significant input voltage variation so the slightly lower voltage of a single cell causes no problems.

Where caution is required is the LARGE voltage difference of using 2 rechargeable (R123 or RCR123) cells in place of 2 CR123. Then instead of 6.5V initially, you are supplying 8.4V to a circuit that may have a max input voltage of 7. This could cause harm to the converter electronics and there are certain lights that strictly forbid it. The 3.0V 123 rechargeables are a specialty, but have a much smaller capacity (600mAh) than CR123s (about 1400mAh) or regular 3.7V R123s (750-800mAh). mAh=capacity=runtime for the most part. one 17670 cell typically has around 1500mAh versus two 3.0V 600mAh 123s, so they would work better in most cases. Some lights like the Night Ops Gladius or Surefire U2 the 2 cell R123 deal is almost guaranteed to cause damage to the light. 

Heres a great article on rechargeable batteries. 

In my early days I annhiliated a custom light which took 3 CR123 batteries and replaced them with 3 R123 rechargeables. 12.6V instead of 9.6V going into the light and the converter went *SIZZLE* and I learned my lesson very quickly. 

Sounds like your VG 2-cell application and 3W LED a single 17670 (also known as a Pila 168 S) is the perfect thing. Go protected if you want hassle free operation, or unprotected if you want more runtime but have to be careful not to overdischarge the cell and ruin it. AW is an excellent source for cells, but domestically there are several dealers, like EMillion, Lighthound, e-electronics.net, battery station, batteryspace, etc. that stock common sizes. 

Hope this helps....


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## Stainless (Feb 1, 2006)

Lunarmodule:

Thank you so very much for taking the time to illuminate me. I find it difficult to accept that there is SO MUCH TO LEARN about even the basics of rechargeable cells.

Reading your post, it is (finally) startimg to sink in.

Thanks again.


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## Lunarmodule (Feb 1, 2006)

Stainless,

Glad I could be of service, its really just paying it forward for all the knowledge I've accumulated here on the Forums on behalf of others willing to give me the necessary schooling on topics of interest. Besides being simple child-like fun, my other primary draw to this hobby interest is the learning potential ingrained in it. Lots to learn, and there are a LOT of exceptionally well educated and/or experienced folks here more than willing to share. I like my lights, but the fellowship displayed here really cements my interest and keeps continually providing new things to explore.

For some reason, maybe because way back when I was a research chemist, batteries have been kind of a favorite subject of mine. Something about the ability to store all that energy in some chemical paste in a can, it fascinates me.

Because I use my lights very often I insist on rechargeables in almost every thing, and if it cant work or is said not to be able to work, I find a way. Disposable cells make sense for a seldom used light or one as a backup or in storage (like a car trunk light). But I personally love the fact that at any time I can just top off the cells and have 100% ready to go, and dont have to fill the garbage can with dead (or partially dead) cells.

One of the trickiest things to know is the initially confusing numbering system for LiIon rechargeables and their corresponding sizes. A great source for this is AW's sales thread in Dealer's corner. Two fundamentals are: 17670 cells are the exact size of 2x CR123, and 2x 17500 cells are the exact size of 3x CR123 for perfect size replacement, as well as having safe voltages. Generally most lights designed for 2 or 3 CR123 cells can use these replacements mentioned without any danger. 

The numbering system works like this: 

17670 cell is 17 67 0
17 is millimeters diameter, 67 is millimeters in length, and 0 is for cylinder

also AA cells are 50mm in length, so 17500 cells are same length as AA and diameter of CR123 (which are technically 17340). 

Then there's the commonly mentioned Pila model numbers, where there are 2 variants, 168 and 150. 168s are 68mm long and 150s are 50mm long. An "S" after the Pila number is a 17mm diameter cell, same as Cr123. An A after the Pila number is 18mm diameter, fatter around and less commonly used (not many lights will take them unless meant for it).

Maybe thats sounds too confusing but for me the key was knowing the numbering system, then it got pretty easy to figure out which cells were interchangeable based on length and diameter.

Other critical issue is unprotected vs protected cells. Stick with protected cells for hassle free operation, they shut themselves off before reaching harmful low voltages and incorrect charging procedures. Unprotected are much cheaper, have more capacity, but can be dangerous if mistreated. One of the biggest killers of LiIon cells is excessive discharge. Unprotected cells, if left running til the light goes out, can be completely trashed with just one instance and trying to revive them on a charger is risky, unlikely, and dangerous. Unprotected are really best for use with high power incandescent applications or other high current mods and they demand careful handling of the user to avoid excessive discharge and cell to cell imbalance problems. Protected are the hot ticket for almost all LED lights.

OK, now I've gone on a bit at length and I sincerely hope none of this is old news to you, but even if it is, it is helpful to anyone new to or not experienced with rechargeable LiIOns. 

It feels good to be appreciated, thanks for posting your gratitude!


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## Stainless (Feb 3, 2006)

Thanks again. I have copied and saved all that info - and the linked article into a Word document for my future study. This is a LOT to grasp.


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## Kelvino (Feb 27, 2006)

Hi,

I'm new to the flashlight scene and after going through this forum for a while now I'm totally infected by all your passion to this hobby.
I just got myself a Vital Gear F2 and a FB1 body, followed by a recently ordered KL1 + F04 set from oldgrandpajack.
Thanks to all of you I got the feeling, the need to order some stuff from Lighthound, too :huh:.

I hope someone of you can help me with this question:
Which of this configuration on a FB2 tube works and has been tried out?
I was thinking of either a protected 17500 or 17650 cell, but I'm confused with all the differences in the actual sizes.

Thanks in advance for your efforts.

Kind Regards,
Kelvin


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## Stainless (Feb 28, 2006)

Riza:

I am curently using a pair of rechargeable CR123A in my FB2. 
It seems to be working well, plus I can use the individual cells in two seperate single cell lights if I want to.

I am truely amazed to find out how much there is to learn about "just" batteries.


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## Kelvino (Mar 2, 2006)

Thanks Stainless, I think I will go with a set of rechargeable CR123A and give the 17500 a try.

Yes you're right, it's amazing what you can learn just about batteries. I wish it would be as simple as in the old Maglight times with simple AA, AAA, C or D-Cells.


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## mdocod (Mar 4, 2006)

just a quick correction: cr123 primary batts are actually about 16mm in dimeter and are actually often refered to as 16340 size cells... MOST bodies designed for cr123 primaries will have enuogh play to fit the larger 17mm cells... The 17670 size was a very tight squeeze requiring "banging against leg" to remove in my ultrafire light... 18mm cells fit only a few lights out there.


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