What's the best method to estimate battery life?

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.

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.

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.

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.

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.

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.

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?

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

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.

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.

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

So like this then?

STL-V6 (2x18650)= 1Amp to the emitter and 2.5hrs battery life
DRY (3x18650)= 1Amp to EACH emitter and 2.5hrs battery life

Nearly, with the STL-V6 you have 1A to the driver, this driver will then reduce the voltage and increase the ampere (Buck driver), i.e. the emitter will get nearly 2A.

The DRY is direct drive and the emitter current is the same as the battery current.

Yes basically recovery voltage, the cells will rise up in voltage once you finish discharging them (remove from used flashlight) all lixx cells do this as with most others. I have some 14500 flames coming for testing.

Back to original post, higher the voltage less the current draw and more run time e.g series lights the mAh stays the same no matter how many cells you use only the voltage increases with each battery you add, this applies to the batteries.

With parallel set ups the voltage will remain the same with no matter how many cells you add just the mAh goes up with each cell in parallel. E.g 2 x 2400 mAh equals 1 x 4.2v 4800 mAh 3 x 2400 mAh equals 7200 mAh 4.2 v cell. But current draw can be higher but it is shared over more cells.

The most common in every day items including flashlights is series, each has advantages and disadvantages. Generally a 2 x 4.2v flashlight in series is 8.4v and if your getting 1.5 amps at the tail cap the driver is getting around 3 amps give or take.

Now we get to C rates 1C = 1 x capacity this can be a max charge or discharge rate or just what your flashlight is drawing.

With the cells we use in flashlights more so with cheaper cells if you draw 1C from a 2400 or 25000 mAh battery you are not going to get the full 1C normally but some cells will and some will not, but RC lipo cells even the little lipo cells i use have a 2C max charge but a 20C max discharge so 20 x 2200 mAh (2.2) so 44 amp max discharge but only can be charged at 4.4 amps.

To work out 1C = 1 x the capacity (mAh) % 1000

So if you read some one discharged a NCR18650A’s 3100 mAh cell at 2C it means 6.2 amps or if you read redilast recommend 1C max charge for 2600 mAh cell it = 2.6 amp but they normally recommend a lower charge rate like 0.3C.

Now working out torch lion batteries C rates is different from my RC but i mention C rates not to confuse people but i feel it is important and has been used for many years before these flash lights and can make things easier once understood and since Ive been getting a lot of PMS about this subject i thought ill post it on here since its about battery life and charging.

Thanks for all of the great information, benckie! I am trying to make a spreadsheet for all my lights. I wanted to have a column for amps per emitter. I thought I would just be able to take amp reading times two for 2x18650 and get that number for a single emitter light. But from this discussion it seems like that isn’t always the case.

If someone would be able to give me a few examples of amps per emitter and battery life (assuming 1amp draw and using 2500mah batteries) for some of the lights I have. Just so I can see it a little easier and have a model to grasp the concept better.

2 x 18650 2500 mAh 8.4v fully charged battery with a tail tap reading of 1 amp will give you approx 2 amps at the driver and 2,5 hours run time.

1 x 18650 2500 mAh 4.2v battery fully charged battery, with a tail tap reading of 1 amp will give you approx 1 amps at the driver and 2,5 hours run time.

Is that more helpful JOE