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
Yes! 
How about a DRY?
Well it depends on what Dry you have.
4 modes ?
Lo——0.1A 25 hours with a 2500 mAh 18650
Mid—0.5A 5 hours with a 2500 mAh 18650
Hi-2.25A 65 mins with a 2500 mAh 18650
Turbo—Direct Drive Max 4 to 5A, since Turbo mode will step down to Hi mode after 20 secs in order to protect driver and emitter from burning no point measuring it.
This is approx it will depend on battery condition, pwm, driver efficiently, if the light is regulated or if the driver is a buck or boost or both, it will also depend on if the flashlights have any low voltage warning and the PCB of the batteries and does not include any lose in the system this goes for all lights.
If the lights your trying to spread sheet are not regulated the current draw will go up as the voltage goes down, this will give a shorter run time, it is not really black and white.
I thought current draw will go up as voltage drops in a regulated light, thus regulating the output current? This happens until the low voltage limit of the driver is hit and then it falls out of regulation so the voltage and current drop along with lumens in a torch.