I have a CREE XM-L T6 1800Lm flashlight I just bought. I've been using 3 aaa NiMH batteries with the adapter. The flashlight will also work with 1 18650 with an included adapter, or 1 16650 with no adapter. Will I see better performance if I use an 18650 or a 26650? Recommendations?

Yes, you will see better performance.

The brightness will be approximately the same as the voltage of 3xAAA vs 1 lithium ion cell is about the same. However, the 18650 probably has three times the energy of 3xAAA cells, so 3x the runtime. It can also handle higher discharge rates better, so it might be a bit brighter and have even more than 3x the runtime.

The 26650 has even higher capacity than the 18650, so even more runtime. Same voltage, so same brightness.

And all that said, there's no way that a 3xAAA powered light is going to put out 1800 lumens. Could it be 180 lumens instead?

As for a recommendation, go for the lithium ion battery. It's a lot more convenient (only one battery to deal with rather than three in their little holder) and it lasts a lot longer. As for which one, that depends on you. Do you already have some of one kind?

I have never experimented using 3 x AAA NiMH battery substitute for 18650 battery, however my hunch is that the answer will be yes depending on various factor as described below.

The maxium discharge rate for the 18650 or the 26650 is much higher than those for the AAA NiMH battery assuming you will be using better know brand 18650 cell like Panasonic, Redilast. Some of the cheaper brand like those from Ebay will only perform limited X amount of current discharge before the internal resistant affect the performance. Even with that, those cheaper brand 18650 still can produce fair amount of current discharge and most likley be more than those of AAA NiMH. This still may not mean you will get better performance from your particular flashlight. It will depend on what the driver that was used for your flashlight. If it is one of the more typical high lumens flashlight where they are driving the LED at a high current, then I can say for sure that the 18650 will be the way to go. It should provide longer runtime and higher current for the driver to drive the LED. If the flashlight has a low current driver and the flashlight spec is one of the lower lumen flashlight, then I will have to say that the 18650 will provide much longer runtime but it will not provide anymore lumen since that is already spec out by the driver. The listing you provide was 1800 lumens which pretty much tells me that it most likely have one of those drivers that drive the LED at 2.5 to 3 amps. In this case, you will benfit from 18650 or 26650. What is your current runtime when using 3 AAA NiMH and does it dim after a short runtime?

The difference between 18650 and 26650 is not much. There are now 3400 mah 18650 battery out in the market while most 26650 are around 4000 mah. There are listed 26650 with much higher rating but I would not trust those listing. If this was to be used as a helmet flashlight, stay with the 18650 mostly because of the weight difference. 26650 is around 100gram and the 18650 with the adapter is about 65 gram. That 25 gram can noticable to some folks when these things are on top of their head. For use as a handle bar light, personally I like to use the 26650 battery instead. For one thing, you can get 26650 4000 mah battery cheaper than the higher quality 3600 mah 18650. One thing worth noting is that the performance from a 4000 mah 26650 will be overall better than from a 3400 mah battery beside the obvious higher rating. The 4000 MAh 26650 can yeild a higher discharge rate than the 3600 mah 18650 and that will help provide less of a voltage sagging which can dim the light.

The claim is that the light "can come to 1800 lumens." With what batteries, i don't know.
All i have is aaa nimh's lying around so that's all i've tried. I haven't had the light long and i don't ride often in the dark so i don't know how long a runtime i'm getting. I'm using it on my handlebars so I'm not so worried about weight. Just whatever works well and is cheapest.

If you get 600 lumens from that light, even with 18650 or 26650, consider yourself lucky. That said, 600 lumens is plenty bright for city riding. And I'd agree that you don't need to worry about the weight unless you're riding in the TdF.

You should get about an hour on high, maybe a little more, with a 18650. If you use a lower setting you'll get more time. I use a 18650/2400mah with an XML-U2 light and get just over an hour, but usually I use it on strobe and get lots more than I've ever needed. I haven't done a long enough ride in the dark yet to test it. I carry a spare battery in any case and I have only used it when I didn't charge up the primary.

I was interested to read about this. I recently bought a 1600lm Cree XML T-6 flashlight (incl two 18650 batteries & charger) off of eBay, and one of those el-cheapo universal handlebar mounts, and while it is BRIGHT (I am not set up to measure lumens; I don't have a lot of faith it is actually 1600, but it seems about as bright as a car headlight), it doesn't last long. At full charge, it is super-bright and the pool of light has sharp edges, at the end of my 1/2-hr commute I'm pretty sure it is less bright, and definitely the edges are starting to soften. After another 1/2 hour it is basically dead.

It's not a big issue, I only have a 1/2 hour commute, only one way is going to be in the dark, and I can recharge every night. And I had low expectations for a chinese light off of eBay, I just wanted to pay only like $25 instead of hundreds for a high-powered light specially-shaped for a bike.

Any idea would I get better runtime out of my cheap light if I paid a little more $$ for some higher-quality batteries? I assume any replacement 18650s could use the same charger? The ones that came with the light say on the side "UltraFire LC 18650 2400mAh 3.7V" full/cutoff 4.2/2.75V

thx for your expertise...

The UltraFire batteries are notorious for overstating their runtime. By a lot. Tests on CPF have shown that their 2400mAh batteries often don't break the 4-digit barrier. Currently the best available 18650s are the Panasonic 3400 series, which are sold in protected form by various manufacturers (EagleTac and Orbtronic, and I think even Int'l Outdoor has some). The other bonus is that the reputable 18650s also have a much longer cycle life, so not only do they have higher capacity they will also keep that capacity through many more charge-recharge cycles. Just make sure your charger is up to the task too; the cheap chargers are known for overcharging batteries/not shutting off. Get a multimeter/voltmeter and make sure the batteries leave the charging cradle when they are at 4.20V. Don't leave them unattended.

Also, 600 lumens from a single XM-L is in the territory where heat buildup starts to be the overriding issue. If your 3xAAA/weak 18650 batteries were holding you back before, make sure to check (touch) the light once you switch to the better 18650s, you may find that the light-head gets very hot very fast. Usually not a significant issue so long as you keep air moving over it, but if the LED itself is not well heat-sinked, you may find its lifespan dramatically reduced.

Thx for the great info. I guess I will shop online for some Panasonic 3400, maybe I can find a kit that comes with a more reputable charger as well (bc I'm not going to be standing around waiting for batteries to charge).

What is "protected"? And what characteristic does mAh measure? Is that supposed to indicate runtime, or power, or ...? (It's been a long time since undergrad physics EM theory...) When you say "often don't break the 4-digit barrier", do you mean it may actually be < 1000 mAh?

I did actually recently buy a (cheap) multimeter, this will be a good opportunity to play around with it! My current charger does have an indicator that goes from red to green, which I assume means it stops charging. I should test them right when they go green, and then another time leave them in overnight and test to see if they overcharge.

As for heat, hopefully I can ride fast enough to keep sufficient airflow! But I don't know about heat-sinking. I don't see any obvious fins or blades or anything like that. The lens is quite thick glass, that seems robust, and the LED is maybe 4-5cm behind the glass, I don't know if an air chamber that size can act as a heatsink or not. Would it be recommended to drill pinholes in the side of that chamber?

I did some research on my own questions there and came up with...

"protected" is good (for regular consumers anyways); the battery includes a circuit with high cutoff (to prevent overcharging?) and low cutoff (to prevent over-discharging?), both of which can be dangerous. (chemical fires, explosions). Mine say 4.5/2.75, so they are allegedly protected.

mAh is milliAmpere-hours. The important thing there is hours; so if you were to draw 1 milliAmp from a fully-charged battery, how many hours until it runs out? 2 milliAmps would be half the time, etc. So basically it measures the capacity of the battery; how much "juice" it can hold (and discharge). Bigger mAh = longer runtime. Mine say 2400, but are possibly actually under 1000.

I found this interesting article at CPF (candlepower forums). Who knew people geek out over batteries as much as we here at BF geek out over bikes?! Anyways, it seems likely that

* my batteries are not truly UltraFire brand, but are
* recycled, re-labeled
* unknown mAh
* unknown "protected" or not
* I should never buy 18650 batteries from eBay.
* This from an american online company looks like it might actually be what my batteries claim to be (UltraFire 2400mAh protected), at $8/ea
* This Tenergy 2600 mAh protected (one of the reputable brands cited above) looks like an even better deal at $7/ea.

Strangely, batteryjunction.com doesn't have any 18650 over 3000 mAh (then again they don't appear to sell any Panasonic either). If somebody else has online sources for 18650 that they recommend as trustworthy, that'd be good to know too.

I use single cell lights with a 3 volt cut-off so I don't worry about the protected circuit. This is a good source for the Panasonic 3400's. https://www.fasttech.com/products/142...0mah-37v-18650
This would be a good charger for that battery with the 2amp charge rate. https://www.orbtronic.com/batteries-c...harging-speeds It will also charge 26650's.

Hmm, that is a better price than I've seen anywhere else, but also that's a chinese company, so after reading that article I am suspicious.

I haven't ever used the 18650 batteries so I can't speak to that. On another note, if the light only has one LED, I don't see how 1800 Lumens is even possible. According to the datasheet from Cree, the XM-L line of LEDs, "...can deliver 1000 lumens..." unless I am reading it wrong. The data sheet I found was here: https://www.cree.com/~/media/Files/Cr...g/XLampXML.pdf

That, plus the fact that they get 100 lumens/watt MAX, means that any light producing 1800 lumens would run out of power on a 18650 battery in about 15 minutes. 2400mahx3.7v = 9wh, OK, maybe 30 minutes. Only that if you're lucky.

It's a pretty simple matter to put two (or more likely four, nine, sixteen, etc.), modules right next to each other. They still look like one LED, but they can make them emit as much light as they like.

And zacster is right about the runtime. And it gets worse if it was powered by 3xAAAs -- instead of 30 minutes of runtime, you'd get like ten, assuming that the batteries could even put out that much power.

This story intrigues me -- 200 lumen/watt LEDs? Yes, please!

But even with 200 lumens/watt, Cree is speculating on real-life lights that will put out over 100, nowhere close to 200. I just bought an LED bulb for my house and it gets 50 lumens per watt.

Cree isn't speculating. They are selling (or will be soon) LEDs that can produce up to 200 lumens/watt. Here's a link to the data sheet.

Now, the "up to 200 lumens/watt" part does require that you put the right amount of current to reach it's maximum efficiency -- but this is true of any LED. It's just that no LED has had a maximum efficiency of 200 lumens/watt before.

So you didn't buy a MK-R bulb. Just because CREE released (or is about to) a new, more efficient emitter, that doesn't mean that existing LEDs will somehow disappear or get magically upgraded.

Side note: the picture at the link I gave shows a unit with four modules (I'm not sure these are the right terms, but it's pretty obvious from the picture that there's four of them.)

How long until these MK-Rs or something like them are in flashlights and/or dedicated cycling lights?

No idea. So far, I don't seem to see these emitters sold anywhere, and the press release went out in December, so I dunno. I don't know how long they usually take, but it's obviously coming.