# how long will 18650 3100mah battery last on xml-t6 led?



## byhsu (Aug 27, 2013)

I bought a light with a CREE XML T6, and i want to buy a Li-ion 18650 protected battery for it. I need it to last me at least 3 hours on High setting. 

I am planning on getting some Generic Batteries with Panasonic cells and 3100mAh capacity, wonder if they will last me 3 hours and how much more would i get out of the 3400mAh capacity? I've seen the 3100mAh for about $8/each shipped and for the 3400mAh is a little over $10/each shipped.

Thanks


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## torukmakto4 (Aug 27, 2013)

An XM-L is an emitter. It does not determine its own drive current or the minimum battery operating voltage. Those parameters are set by the flashlight's driver.

What is the light, exactly?


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## byhsu (Aug 27, 2013)

torukmakto4 said:


> An XM-L is an emitter. It does not determine its own drive current or the minimum battery operating voltage. Those parameters are set by the flashlight's driver.
> 
> What is the light, exactly?



don't know, is from ebay. says 1600 lumens, but i don't think they go up that high, i saw another listing for a similar one with 10 W LED, so I assume is one of those.


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## StorminMatt (Aug 28, 2013)

Assuming we're talking about a fully driven XM-L (ie 3A), you will NOT get three hours from a 3100mAH battery. You should expect more like an hour (plus or minus). You may have a lower mode which would allow the light to last three hours. But this would require that your current draw be only about one amp, which would only give you maybe 300-400 lumens.


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## byhsu (Aug 28, 2013)

StorminMatt said:


> Assuming we're talking about a fully driven XM-L (ie 3A), you will NOT get three hours from a 3100mAH battery. You should expect more like an hour (plus or minus). You may have a lower mode which would allow the light to last three hours. But this would require that your current draw be only about one amp, which would only give you maybe 300-400 lumens.



What if it was a 3400mAh battery?


Thanks


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## konig (Aug 28, 2013)

It is only 9% difference between 3100mAh and the 3400mAh battery so don not expect it to be much better.


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## AnAppleSnail (Aug 28, 2013)

Your question is sort of like asking how many meals a big takeout plate of spaghetti will provide. Even with a weight of spaghetti, we don't know how quickly you eat it!

Battery life is roughly equal to (Battery Capacity) / (Current Draw from Battery). We can make some ASSumptions about these "1600 lumen" lol-lights in general. I'd guess the actual current is somewhere between 1 to 1.5 amps, the actual lumens somewhere between 300 and 600, and the 'full output' to last about one minute before thermal droop happens. That gives us a wild-A**-guess of a runtime between two and four hours, depending on how loosely the manufacturer claims are made.

An actual-1600-emitter-lumen output XM-L based flashlight would require considerable expensive architecture (Direct-soldered bare LED on massive copper block with five to six amp current) and have runtime of a few minutes per 'burst,' half an hour total.


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## mattheww50 (Aug 28, 2013)

Actually I doubt that 1600 lumens is even possible with an XM-L T6. That would probably require ~25 watts drive power. Unfortunately there is no mention of the flashlight involved, so we have no idea
what high is , but realistic maximum output for an XM-L T6 is probably around 900 lumens. That would require ~12 watts, and would require extensive thermal management. A 3100mAh cell contains stores about 11 watt hours of energy. So if you if make some assumptions (which are admittedly, exactly that) we can 'thumbnail' the result. 

So lets say the output is about 750 lumens (and without very extensive thermal management that's probably close to the upper limit on an XM-L T6), that is going to require ~9 wats into a 'good' driver, so figure a little better than 1 hour run time for eash 3100 mAh 18650 cells in use. If you want 3 hours from a single 3100mAh 18650, the output going to have to be limited to something around 300 lumens.


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## Chodes (Aug 28, 2013)

This is very simple maths. 3100mAh. Call it 3000mAh for simplicity.
3000mAh = 3Ah, = 3 Amps for 1 hour. Or 1 Amp for 3 hours.

So if you want 3 hours from your 3Ah cell, you need to limit current draw to 1Amp. As matheww50 pointed out in previous post, that will be around 300 lumens max.

There is a good chance you're "1600 Lumen" light is drawing somewehere between 2 and 3 amps so is putting out 500 - 900 lumens.
A Malkoff Hound Dog will put out around 100 lumens continuously, but with 2 x 18650 3400mAh cells will last around 1 hour 45 minutes.

Regarding the 3100mAh to 3400mAh run difference, that's also very simple. 300 is about 9% of 3100. 3100 + 300 = 3400. So 3400 will last around 9% longer than 3100mAh.


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## LeeBrown72 (Sep 10, 2019)

byhsu said:


> I bought a light with a CREE XML T6, and i want to buy a Li-ion 18650 protected battery for it. I need it to last me at least 3 hours on High setting.
> 
> I am planning on getting some Generic Batteries with Panasonic cells and 3100mAh capacity, wonder if they will last me 3 hours and how much more would i get out of the 3400mAh capacity? I've seen the 3100mAh for about $8/each shipped and for the 3400mAh is a little over $10/each shipped.
> 
> Thanks


Hi,
I'm a Laser engineer and a flashaholic. I have about 50 various LED flashlights of every size, configuration and battery type.
That being said, a T6 LED draws about 3A (3000mA) of power per hour to operate on high beam. That's 3 amps per hour of draw (battery drain). A 3100mAh 18650 battery, depending on its quality, operates in a range from 4.2V (fully charged) to around 2.7-3.2V (discharged or automatic shut-off if it has a PCB, or if the flashlight has a PCB to protect the battery from over-discharge). So a good quality 18650 3100mAh battery gives you a "usable" 1.75-2Ah of energy at its nominal 3.6-3.7V of output. So you can calculate that you'll get about 30-40 minutes of high-beam usage before the flashlight goes dark. A 3400mAh Panasonic NCR18650B (a very good quality, high capacity, affordable Li-ion battery) will give you just over an hour of runtime.
Also, keep in mind that the flashlight's beam will get weaker as the battery is drained down from 4.2V to let's say 3V, i.e. it'll get dimmer.
My favorite everyday-carry flashlight has a T6 emitter and uses a 26650 Battery. I prefer the KeepPower IMR26650 5200mAh battery. Very good quality, affordable and a much longer runtime.
I do not sell or work for any battery or flashlight company. All my knowledge just comes from years of trial and error *experimentation*.
Anyway, just make sure you get a "CREE" LED, a good quality flashlight, and the best high capacity batteries you can buy. It's pretty hard to go wrong if you do.
Have fun!


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## alpg88 (Sep 10, 2019)

mattheww50;4270382[B said:


> ]Actually I doubt that 1600 lumens is even possible with an XM-L T6. [/B] That would probably require ~25 watts drive power. Unfortunately *there is no mention of the flashlight involved,* so we have no idea
> what high is , but realistic maximum output for an XM-L T6 is probably around 900 lumens. That would require ~12 watts, and would require extensive thermal management. A 3100mAh cell contains stores about 11 watt hours of energy. So if you if make some assumptions (which are admittedly, exactly that) we can 'thumbnail' the result.
> 
> So lets say the output is about 750 lumens (and without very extensive thermal management that's probably close to the upper limit on an XM-L T6), that is going to require ~9 wats into a 'good' driver, so figure a little better than 1 hour run time for eash 3100 mAh 18650 cells in use. If you want 3 hours from a single 3100mAh 18650, the output going to have to be limited to something around 300 lumens.



there kinda is, 1600lm t6 is most likely not even xml, but LB led, they are usually used in cheap lights that Chinese manufacturers make in abundance. in the real world that light most likely 1-1,5A 400lm at best, it would run about 2 -2.5hours, on 3400mah cell, lights like that have no thermal control, no timer, most likely simple linear driver. so there will be no stepdowns.
the rest of you post i agree,


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## Top Shirt (Sep 26, 2019)

A simple math question: A light has 4 18650 cells in series or parallel at 3500 mAh each. Combined do they equal 14000mAh or 14A's? So would that equal 14amps for 1 hr or 1 amp for 14hrs also? Sorry if this is a stupid question but I'm new at this game. This old dog is just trying to learn new tricks!! lol Great forum guys. thanks Rob


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## alpg88 (Sep 27, 2019)

Top Shirt said:


> A simple math question: A light has 4 18650 cells in series or parallel at 3500 mAh each. Combined do they equal 14000mAh or 14A's? So would that equal 14amps for 1 hr or 1 amp for 14hrs also? Sorry if this is a stupid question but I'm new at this game. This old dog is just trying to learn new tricks!! lol Great forum guys. thanks Rob


yes, pretty much, but only in parallel wiring, 
with series you add up voltage, but capacity remains the same, 3500mah.


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