# What's the best method to estimate battery life?

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-JOE-
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What's the best method to estimate battery life?

I was wondering if there is a formula that is fairly accurate at determining a flashlight's battery life?

scaru
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Well you can use a multimeter to measure the current draw and then use that.

kramer5150
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The simplest way I have found...

Use a hobby charger with a discharge feature, to approximate the cell storage capacity in Amp-hours.

Charge cell and measure the tailcap current draw in Amperes.

divide cell capacity by current draw to get an approximate number of hours.

It only works though if the tailcap current draw matches the current draw of the charger (in the first step above).  Cells will almost always have a higher capacity with lower current draw applications.

pounder
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this is a pretty good calculator..

http://www.kenworster.com/ledcalc/

kreisler
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on Hi-mode the runtime of your flashlight is not more than 1h (unless it's a phoenix)

solly fol trolling

*FMI* i got 4 i/o sh
-JOE-
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I am doing all of my flashlight tests with Trustfire Flame 3000mah batteries. I have a hobby charger (IMAX B6) but I don't think it is very accurate.

I'm confused about determining the "usable" capacity (there's probably a better term) of the batteries. Like the amount of mAh between 4.20v and PCB cut-off (not sure what voltage that is either, 3.0v?)

-JOE-
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kramer5150 wrote:

The simplest way I have found...

Use a hobby charger with a discharge feature, to approximate the cell storage capacity in Amp-hours.

Charge cell and measure the tailcap current draw in Amperes.

divide cell capacity by current draw to get an approximate number of hours.

It only works though if the tailcap current draw matches the current draw of the charger (in the first step above).  Cells will almost always have a higher capacity with lower current draw applications.

This seems like a great method. It would also be very accurate.
benckie
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This is easy very simple math

A 2400 mAh battery = 2400 milliamp hour. so 1 amp is 1000 milliamp. 2400 mAh is 2.4 Ah so a 2400 mAh 18650 battery will be able to give 2.4 amps over an hour.

If you have a XP-G light that has a current draw of say 1.2 amps at the tail cap with a digital multi meter. So using a 2400 mAh battery will give you 2 hours run time.

It helps if you know the TRUE mAh of the batteries you are using, say the 3000 mAh flames are around 2600 mAh.

Another way is to gun the light on high with a fully charged battery in front of a fan and time how long it last.

The best way has to be a decent hobby charger, fully charge the battery and set the cut off to the same as the protection cut off the battery or the torches driver low voltage warning and discharge the battery at the same current as the torch uses till the charger cuts off then use the math from above, but this will depend if your driver is digitally regulated and stays at the same current draw from start to finish. This will tell you the TRUE usable mAh of the battery in that particular torch.

The math is the easiest and quickest way thats pretty dam close, unless your using cheap ebay batteries with 50% of the claimed mAh.

-JOE-
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benckie wrote:

The best way has to be a decent hobby charger, fully charge the battery and set the cut off to the same as the protection cut off the battery or the torches driver low voltage warning and discharge the battery at the same current as the torch uses till the charger cuts off then use the math from above, but this will depend if your driver is digitally regulated and stays at the same current draw from start to finish. This will tell you the TRUE usable mAh of the battery in that particular torch.

That's the method I am going to try but I don't know at what voltage the PCB kicks in.

benckie
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Good trustfires its around 2.75 volt, cheap ultrafires of ebay it is around 3 volt, redIlast under 3100 is 2.75 and redilast 3100 is 2.5 volt, solarforce and hi-max im unsure, some pamisonic 3100,s with cheap protection is around 3 volt.

Hobby chargers realy come in handy for this but basic math will give you aprox

-JOE-
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That seems pretty low. I know at least for lipos that going under 3.0v is a big no-no. I take it Li-Ion can be taken down much lower?

benckie
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Yeah li-ions can go lower and the built in protection is oftern lower then 3 volt. The old train of throught was 2.7v per cell min for lipos now its 3.2 volt min per cell and some new ESC cut out higher. The batteries seam to last longer and the internal resistance stays lower for longer

I used to test my li-ons to 3 volt as habbit and most my torches cut off around 3 to 6 volt but the guys on the forum spoke up so now i go below 3 volt to try and help every one.

benckie
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Another thing to take into accound while working out the run time of a certain torch with a certain battety is, the higher you discharge the battery the less mAh the battery will give.

So if you discharge a 2400 mAh 18650 @ 3 amps it will not gove the full mAh its will give around 75% of the claimed mAh (2400) i was not going to bring this up as i felt the math was close enough.

There is so many factors in this, DDM's, batteries, the charger, the flash light its self, the user and where the batteties are brought from and there protection PCB's.

A hobby charger reall helps with this this as you will know the battery cut offs and excatly what the battery will do under the same draw and the bettety the battery the more it can give.

HKJ
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benckie wrote:
So if you discharge a 2400 mAh 18650 @ 3 amps it will not gove the full mAh its will give around 75% of the claimed mAh (2400) i was not going to bring this up as i felt the math was close enough.

That is not correct, but depends on the actual chemistry in the cell and what cutoff voltage you use.

Here is one example of a battery where the capacity difference is very low between different currents:

My website with reviews of many chargers and batteries (More than 1000): https://lygte-info.dk/

benckie
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HKJ, I was thinking more along the lines of trustfire cells i used a 2400 mAh 18650 trustfire flame as an example and under rated my results. The reason why i used 18650 trustfire flames 2400 mAh as an example as JOE who asked the question said he was using 3000 mAh 18650 trustfire flames that we know only test between 100 to 200 mAh more, so the results would be closer and they are the closest batteries i have to what JOE was talking about. The results would be different with sanyo, panisonic, IMR or 26650 cells.

2400 mAh trustfire flame: 3 amp discharge test from fully charged to 3 volt.

I thought this was more relivant. There is so many factors in this, DDM's, batteries, the charger, the flash light its self as each flash light, even the same
Model may vary, the user and where the batteties are brought from and there protection PCB's and the flash lights driver efficiency.

The general info on here will give a basic aprox run times for flash lights based on the current draw on the tail (switch). I have done a few 0.5 amp, 1 amp and 3 amp discharge test,s on the 18650 2400 mAh trustfire flames since they test really close to the 3000 mAh flames you should get a ruff idea with a bit of math and a current draw test on your torch.

Manny
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Run On Full Until empty and  Check how long it took to kill t h e m.......

HKJ
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benckie wrote:

HKJ, I was thinking more along the lines of trustfire cells i used a 2400 mAh 18650 trustfire flame as an example and under rated my results. The reason why i used 18650 trustfire flames 2400 mAh as an example as JOE who asked the question said he was using 3000 mAh 18650 trustfire flames that we know only test between 100 to 200 mAh more, so the results would be closer and they are the closest batteries i have to what JOE was talking about. The results would be different with sanyo, panisonic, IMR or 26650 cells.

It depends very much on the batteries, I did test some good 3000mAh and some not so good 2400mAh:

Also try placing a line at 3 volt, you will see the difference at different currents is greater, especially on the 2400 battery.

You might also see a few batteries where the mAh is slightly greater at 3-5A current.

My website with reviews of many chargers and batteries (More than 1000): https://lygte-info.dk/

benckie
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I see whay you mean, your 2400 flames did not test to well at all, but the 2600 (3000 flames) seam about right, nice snd grouped. Where did you get your 2400 flames from DX ?

As i found the manafont trustfire flames tested higher in the mAh department then DX and with the 3000 & 2400 mAh flames brought from manafont there was less then 200 mAh between them as the best 3000 mAh flame tested just over 2600 mAh and the best 2400 was not far behind.

I brought a few trustfire flame 3000's for my old but since i was not getting more then 200 mAh more i whent back to buying the 2400's as to me it was not worth the extra buck for a few seconds more run time.

Any way your graph is much better then my data table as is has all the diffrent current draws on it so say if the flash lights low voltage kicks in at 3 volt like you say run a line across it and there you go.

My data table just shows if you gun a trustfire flame 2400 in a light with a 3 amp drop in you will get 42 mins run time to 3 volt.

So JOE not knowing what torch your testing if it has a low votage warning or if it is a muti cell light, you can use HKJ's graph or you can use your imax b6 set it to discharge at the same current draw as your light with the same cut off as the torch or 2.75 volt for the battery and discharge the battery, when done the charger will tell you how many minuets i took and how much mAh the battery gave.

If your unsure of the cut off voltage most off my singe cell lights have a 3 volt warning or none the light might dim, my muti cell lights is around 6 volt for 2 x 18650's. So 3 volt or 2.75 is a good starting point just make sure the cell is full charged and rested before discharge.

If you notice you discharge a battery to 3 volt then once the charger stops and the volts rise up to 3.3 volt thats normal they do that and the longer they rest generaly the higher they climb back up.

HKJ
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benckie wrote:

I see whay you mean, your 2400 flames did not test to well at all, but the 2600 (3000 flames) seam about right, nice snd grouped. Where did you get your 2400 flames from DX ?

The 2400 was from DX and the 3000 was from Manafont.

In the reviews I have also charts that directly shows the runtime, here is one of them:

But that is only correct for lights with a constant current consumption, in most lights the current will vary with the voltage.

My website with reviews of many chargers and batteries (More than 1000): https://lygte-info.dk/

benckie
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The time in mins has to be one of the most important graphs and why i use data tabes.

HKJ
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benckie wrote:

The time in mins has to be one of the most important graphs and why i use data tabes.

For these data I prefer charts, it is much easier with all the runtimes in the same chart and you can interpolate very fast. I.e. a light that uses 2.5A and works down to 3 volt, it only takes seconds to estimate runtime from the chart.

I do have many megabytes of tables for each battery, but I seldom look in them.

My website with reviews of many chargers and batteries (More than 1000): https://lygte-info.dk/

Jinx
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Manny wrote:

Run On Full Until empty and  Check how long it took to kill t h e m.......

This beats all the other more complicated ways being mentioned. If you need to know the runtime of a specific cell and torch, just test it!

Ps this min voltage cutoff, do any of you guys adjust your cutoff voltage relative to current draw? Manufacturers of certain batteries specify it is safe to go to a lower cutoff under shorter tests or higher under longer tests. Not sure if this applies to 18650s but i imagine it will without checking.

-JOE-
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HKJ wrote:

In the reviews I have also charts that directly shows the runtime, here is one of them:

But that is only correct for lights with a constant current consumption, in most lights the current will vary with the voltage.

Nice graph! There has been a lot of helpful and insightful information in this thread from everyone.

HKJ, it appears that the TrustFire 3000mah batteries PCB kicks in at 2.8v, correct? Also you wouldn't happen to have a formula for the discahrge time would you? Just to figure runtime on lights don't pull exactly 1.0 ,2.0 , 3.0, etc.

apt323
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benckie wrote:

Good trustfires its around 2.75 volt, cheap ultrafires of ebay it is around 3 volt, redIlast under 3100 is 2.75 and redilast 3100 is 2.5 volt, solarforce and hi-max im unsure, some pamisonic 3100,s with cheap protection is around 3 volt.

Hobby chargers realy come in handy for this but basic math will give you aprox

I have some Flames 14500's from MF they go into low voltage protection at 3v, or that is the measured voltage of the cell when i pull it out of the light. I guess that voltage could be a recovery voltage since there is no load at the moment?

HKJ
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-JOE- wrote:

HKJ, it appears that the TrustFire 3000mah batteries PCB kicks in at 2.8v, correct?

No, my test stops at 2.8 volt, the protection is at a lower value.

-JOE- wrote:

Also you wouldn't happen to have a formula for the discahrge time would you? Just to figure runtime on lights don't pull exactly 1.0 ,2.0 , 3.0, etc.

That is easy: capacity/current, you select the mAh from the curve closest to the actual current draw (From the capacity chart) and then divide with the actual current draw.

For the TrustFire 3000 you would just use 2500mAh and with 2.5A draw, the time would be (mAh must be converted to Ah) 2.5Ah/2.5A -> 1h.

You can also just look at the "discharge time" curve and guess, that will probably be just as precise. (The variation in current draw with voltage spoils any precise calculations).

My website with reviews of many chargers and batteries (More than 1000): https://lygte-info.dk/

-JOE-
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HKJ wrote:

That is easy: capacity/current, you select the mAh from the curve closest to the actual current draw (From the capacity chart) and then divide with the actual current draw.

For the TrustFire 3000 you would just use 2500mAh and with 2.5A draw, the time would be (mAh must be converted to Ah) 2.5Ah/2.5A -> 1h.

You can also just look at the "discharge time" curve and guess, that will probably be just as precise. (The variation in current draw with voltage spoils any precise calculations).

This method is my original method but it just doesn't seem very accurate. Or is 2500mah really the "usable" capacity of these batteries? I mean I know they can hold that. I just assumed that the "usable" value (or until ~3v) would be a least 100mah less than overall capacity.

HKJ
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-JOE- wrote:

HKJ wrote:

That is easy: capacity/current, you select the mAh from the curve closest to the actual current draw (From the capacity chart) and then divide with the actual current draw.

For the TrustFire 3000 you would just use 2500mAh and with 2.5A draw, the time would be (mAh must be converted to Ah) 2.5Ah/2.5A -> 1h.

You can also just look at the "discharge time" curve and guess, that will probably be just as precise. (The variation in current draw with voltage spoils any precise calculations).

This method is my original method but it just doesn't seem very accurate. Or is 2500mah really the "usable" capacity of these batteries? I mean I know they can hold that. I just assumed that the "usable" value (or until ~3v) would be a least 100mah less than overall capacity.

That is the reason I say you must check the discharge curve to get the real capacity and us a curve close your actual current level.

My website with reviews of many chargers and batteries (More than 1000): https://lygte-info.dk/

-JOE-
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I am confused about flashlights that have 2x and 3x batteries.

For example a 2×18650 with a tail-cap reading of 1Amp. Using 2500mah batteries. What would the estimated battery life be? 2.5hrs or 5hrs?

HKJ
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-JOE- wrote:
I am confused about flashlights that have 2x and 3x batteries. For example a 2x18650 with a tail-cap reading of 1Amp. Using 2500mah batteries. What would the estimated battery life be? 2.5hrs or 5hrs?

For batteries in series (This is the most common configuration) it would be 2.5h.

My website with reviews of many chargers and batteries (More than 1000): https://lygte-info.dk/

-JOE-
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Ok, so lets say my STL-V6 gave me a tail-cap reading of 1Amp. That would mean the emitter is getting 2amps and the estimated battery life would be 2.5hrs.

What about a 3×18650 (DRY battery configuration) with a tail-cap reading of 1Amp using 2500mah batteries?

HKJ
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-JOE- wrote:
Ok, so lets say my STL-V6 gave me a tail-cap reading of 1Amp. That would mean the emitter is getting 2amps and the estimated battery life would be 2.5hrs. What about a 3x18650 (DRY battery configuration) with a tail-cap reading of 1Amp using 2500mah batteries?

That is also a series connection, both batteries and leds, i.e. the current is 1A in all batteries and all leds. Again the estimated runtime would be around 2.5h

My website with reviews of many chargers and batteries (More than 1000): https://lygte-info.dk/