Mystery - Replace 3xAAA battery carrier in TechLite Lumen Master 250 with 18500


I had seen references in various places about the possibility of replacing the 3xAAA battery carrier in a TechLite Lumen Master 250, with an 18500. These are the latest version of the lights that are sold as 3-packs at CostCo.

Anyway, I’ve been trying to do that (replace the 3xAAA carrier with an 18500), but failing miserably :(… I originally started posting about this in the following thread in the “Batteries” section of CPF:

I have pics, etc. on that thread, and, as I said on that thread, I’m stuck at this point, and, even just logically, I don’t have any idea why what I’ve tried would not work, including:

- Replace carrier with an 18500 + magnet

  • Jumpering from the 18500 (both with and without magnet) to the light.

If anyone has been able to actually do this, please post, because this has been driving me nuts :(!!

NOTE that I’m talking about the 250 version, which is the one that I have.


Drop the carrier (with batts) in and see if you can ground the neg end to turn light on (switch on if side switch). Use wire, or DMM set to measure amps draw. Now do the same with the replacement battery.

If that doesn’t work for both, then there is a problem at the positive end. Use wires with magnets on each end to make connections, instead.

Only after you know the battery is working, then you can resolve any fitment/continuity issues and confirm whether at the positive and/or negative ends.

For difficult problems, break them down to one issue at a time . . .

I’m not sure it’s really a mystery tbh. :wink:

All you need to do is hook up the battery terminals to the right bits of the torch to complete the circuit.

As you have the originally carrier you can easily test the torch to make sure it works and eliminate that as a problem.

As you had a DMM you can test the battery and eliminate that as the problem too. Therefore logic says it’s likely to be the contacts.

Looking at this pic:

It looks like the original carrier has a small pin to make contact to terminal. Even with your magnet mod later on, it still looks too big and based on this:

I suspect it still isn’t making contact.

Personally I’d just run the light on some eneloops or lithium primaries. A li-ion isn’t really going to provide any real benefits IMO, not for this light in this guise.


For the record: A user on CPF suggested trying a different battery, a 14500, instead of the 18500 (with the same magnet on the button), and I just did that, and it works!!

He’s suggesting that the 18500 that I have may not be able to support the load (i.e., a bad 18500), which is also what I think at this point.

I don’t think that it’s 18500s in general, but that the one specific battery I have is bad (bought from Amazon), so I’ll probably try to find another one later.



BTW, I had tried jumpering the 18500 battery directly earlier, which didn’t work, even though jumpering the carrier worked, which got me kind of stuck. As I mentioned in the CPF thread, I think that I was too quick to dismiss the possibility that the 18500 itself might be bad.

Lesson learned.


Sometimes we just get blocked . . . that was the right time to try another lion so good suggestion and finding. Congrats!

So I am assuming that at this point you may not have access to a DMM to test the voltage of the 18500 to see if it is dead or not….that would be some useful info. A li-on is dead at under 3 volts.

But otherwise, consider that the Techlight is not designed to use a li-on cell, the battery chamber is designed around a battery carrier that has a spring at the positive end to complete the circuit.

So if the battery is ok, I would suspect that the positive end is not making contact even with a magnet installed, because there is a shoulder at the end of the tube that will limit the forward movement of a 18500 cell.

It might take more than just one magnet, perhaps 3/16” or more of magnets stacked up to bridge the gap in order to make + contact. The 14500, being narrower, fits inside the rim of the shoulder.

There is no reason not to use the 18500 if you can solder a spring to the emitter board, or put together a workable battery carrier that will adapt to the 18500 form factor, but I wouldn’t recommend running the light with magnets, or using magnets for more than a test… it would be easy for a magnet to slip and cause a short in normal usage.


I have a voltmeter/DMM :), and reported voltages on the other thread. That 18500 measured, and still measures ~4.15V unloaded.

The magnet that I used is a single magnet, rather than a pile of discs, so it actually seems pretty secure, but when I have time, I’ll try to see if I can do what you suggest. Soldering is no problem, but I don’t have a strap wrench to pull the head off (yet). This was more of an experiment.

BTW, the nice thing about using the magnet is that I can still go back to the 3xAAA carrier anytime, since I haven’t altered the light at all at this point. I could even return it to Costco (but won’t!).


As long as the shorter battery is making contact at the + end it should work. You might be able to fashion a 1/4” long round wooden spacer with a spring on the front to compensate for the shorter battery, and a piece of pvc pipe or a plastic cylinder, or rolled up cardboard with the right dimensions to center the battery in the chamber would work.

Top Cat,

I’ll probably be getting some of these:

and cutting them in half (to half-length) to use a sleeves, once I find some 18500s that work well.