(Noob) Fenix TK15 Battery Question/Problem

So like it says, i'm still pretty new to flashlights/batteries but learning. I run a Bar/Nightclub and have used the TK15's for myself and all my security. We have used about 10 of them over the years and I buy rechargeable 18650's for them and recharge them for the guys when needed with a Pila charger.

I have never had a problem until I just recently bought a used TK15 form a forum. It wont seem to work with an 18650, but I tried two 123A's and it does. Just wondering why that might be, never had a problem before.


And a side question... what is the application for 3.7v 123A's over the 3.0v?

Thx.

Not sure about the first problem, but there are (at least) 2 reasons that people use 3.7 V RCR123. Firstly, in single CR123 lights that accept them, they are an easy rechargeable option over expensive CR123s. Some dropins take 8.4V volts to get them going properly. These are ideally designed for 2x 18650 batteries. Using 2x 3.7 V RCR123 batteries lets you run them in a smaller package, but with less runtime (fully charged li-ions are about 4.2V each).

For your initial problem, did you try other 18650s?

A protected 18650 is longer than two CR123s. You might find that the battery tube is slightly too short for the 18650 you are using in this particular example. I have had this with a TK21 where I could not use a protected 18650 and had to use only unprotected cells.

If this is the reason, you can either use CR123 or unprotected 18650, or what I ultimately did was make a very simple battery tube extension. Using a bit of solid core mains cable, I took a length of the stripped copper core and wrapped it round a 18650 cell. Trimming it to length, this forms a copper ring which you can drop into the tailcap and effectively extend the battery tube slightly. This is often enough the make the connection and allow you to operate the light with protected 18650.

Hmmm, I had a feeling the more I research the more confused I might get, lol. Sorry for the Super-Noob questions but I guess I should start asking/learning here. Now I have lots of questions... please let me know if I should start multiple posts. I underlined my questions to be less confusing.

(After reading all night I also realized I should be very specific on battery type i'm using as well)


So to clarify, I have used different 18650's BUT they are all "protected". The fact that it works with the two RCR123A 3.0V's might back up the "tube-length" hypothesis I guess. Is it weird that ALL my other TK's work with 18650's but this one does not?

I do not completely understand the length problem and i'm confused. I'm assuming the "battery tube" is the tube of the flashlight that the battery is in. Wouldn't the tube length be "too long" to facilitate a no contact problem and the battery too short?... I do not understand how a "protected" battery that is longer than a normal one would have no contact and need the "copper coil trick", wouldn't it be "stuffed" into the tube being too long?

Also, using the "coil-trick" you mention, I see that there is a spring in the tail-cap, so does the little coil you make actually sit "around" the spring?... in other words, i'm assuming the negative side of the battery can contact the metal around the spring and not the spring itself? Does that make sense, am I way off in my understanding?

And for the voltage question, I realized I probably should be more specific. I have some RCR123A 3.0V LIFePO4's and Rechargeable 3.6V Li-ion's. I guess CR123A is the same as 16340's?.. which is the proper term?
So if the flashlight/bulb can handle the voltage, it might be better to always run the higher voltage (3.6V Li-ion's) batteries? In other words, always running near max voltage allowed?

And i'm looking for the voltage specs on the TK15 and can't find them, where's a good resource or am I blind?

Thanks for the advice and the patience, I love to read but not always sure what to search.

So I actually just found the specs on the TK searching "TK15 Manual" and I see the battery recommendations.

But how do you know without a manual what batteries to use when it just says "Use 2xCR123's".. are those 3.0V or 3.7V?

And I answered the CR123 vs. the 16340 question. Sorry, shoulda' searched more, got a lil excited. I'd edit my question but don't think I can because of my post count.

You can edit your question, just click edit at the bottom of your post.

Norm

DosDiablos said:

So to clarify, I have used different 18650's BUT they are all "protected". The fact that it works with the two RCR123A 3.0V's might back up the "tube-length" hypothesis I guess. Is it weird that ALL my other TK's work with 18650's but this one does not?

I do not completely understand the length problem and i'm confused. I'm assuming the "battery tube" is the tube of the flashlight that the battery is in. Wouldn't the tube length be "too long" to facilitate a no contact problem and the battery too short?... I do not understand how a "protected" battery that is longer than a normal one would have no contact and need the "copper coil trick", wouldn't it be "stuffed" into the tube being too long?

Also, using the "coil-trick" you mention, I see that there is a spring in the tail-cap, so does the little coil you make actually sit "around" the spring?... in other words, i'm assuming the negative side of the battery can contact the metal around the spring and not the spring itself? Does that make sense, am I way off in my understanding?

Click to expand...

The tailcap has two contacts. The central spring, and the bare metal surrounding the spring. The battery negative terminal contacts the spring and the battery tube has to contact the exposed metal ring.

If the battery tube is too short compared to the battery, the battery will protrude from the battery tube preventing the tube from contacting the tailcap. Adding the copper ring inside the tailcap (positioned so that the battery tube will sit onto it), makes the tube effectively a bit longer.

It would not surprise me if this one TK15 had a slightly shorter tube. Manufacturing tolerances are exactly that tolerances, so there will be differences from one batch to another.

I don't think the TK15 can use 2xRCR123 (the rechargeable li-ion CR123s), but is limited to 1x18650 or 2xCR123 (primary/disposable cells).

Thank you for the detailed explanation, i understand the length issue now. Didn't realize the tube was actually part of the circuit.

You're right, in did notice the manual does not list RCR's as acceptable. That"s actually what i tested it with and they work, is there a safety issue or a fitment issue?

Again, thnx for your time.

Regarding 16340 vs RCR123.

16340 is a battery size. 16mm by 34 mm, the 0 indicating it's a cylinder. CR123 batteries are disposable lithium batteries of this size. Li-Ion rechargeables also have this size, but can have different chemistries, such as Lithium Phosphate (the 3V rechargeables), IMR (rechargeable, much higher current draw possible) and ICR (the 3.7 V rechargeables that most people probably use).

From what I can see, the ICR seem to have higher higher capacities than the other rechargeables. I just use them in single 123 lights that can take them.

It makes it a little more confusing, but people tend to just call the disposable ones CR123 and refer to all of the Li-Ion ones as 16340 or RCR123. Well, from my experiences here anyway.

DosDiablos - I think Subwoofer is right. Fenix usually anodises tail caps so that you can quarter turn the tailcap and the light stays off. It seems your battery protrudes enough so that the tailcap doesn't fully close and this feature becomes an annoyance.

Try contacting Fenix and explaining to them that you're trying 18650s that work on other versions of the same torch. Maybe you can get a new battery tube.

Actually, before you contact them, try swapping the tail with another one and then the body with another one. That should tell you which part you need replaced.

Always like to provide an answer to help other Noobs that might ever have the same question. The tube was indeed to short. I tried the the copper wire trick and it works fine with the 18650. I ended up just using the rechargeable RCR123A LIFePO4's as I read multiple places they were pretty safe in the Fenix.

Thanks for all the help, i'm learning a ton.