Hi, i have a Fenix TK15 that I use for everything, I haven't had it long but its a great light. I used to have a TK12 I used on my rifle for night shooting and had to have another Fenix after selling it a few years ago.
Anyway, my problem is, it doesn't seem to last long before dropping down to low output mode.
Im not very clued up on batteries. I cant remember how much the UltraFire 3000mAh 18650's I use in it cost but I don't think they were a lot. Is this the reason the light doesn't last long? The charger I have is really basic with just a light that turns green to indicate charge is full (cheap chinese eBay thing). Anyway, my question is = Do I need a protected battery? and what would be a good recommendation 18650 to use in the TK15?
thanks,
Rob.
The reason is probably related to one of two issues:
1) That you are using "Fillintheblank Fire" anything.
IE: There's essentially no such thing as a 3000 mah 18650, its probably some used laptop battery repackaged and sold as a new cell, etc (A lot are at least).
The real cells in that mah range are typically 2600, 2900, 3100 3400 mah. Those ranges are based to a large degree on the chemistry of the cell itself. (Hence the clue as to it being a fake cell if its some other number, etc...)
When you see a cell labeled as something higher than or lower than those ranges (Until the 3600 mah come out, etc...) it means they took a (typically) lower mah older cell, and just CALLED it a higher mah to sell it for more.
If lucky, it was a NEW cell, maybe a 2000 or 2200 mah cell, that they put a 3k mah wrapper on and sold it as a new 3k mah 18650....so it would not WORK well, but it might not be as dangerous.
If UNLUCKY, it was a used (anything) cell that they did the same thing to. That's because the used ones have unpredictable internal resistance, and if you have cells in series, (as can be the case for for multi-celled lights), the DIFFERENCE between two cells in series can lead to a lot of heat, and, over drained and/or runway thermal events, etc (Bad things)
If the cells are also UNprotected, well, its just making whatever might have happened more likely to happen. (Not good)
The cheap ebay charger might be fine, or, killing the good cells/making the bad cells worse by using a poor charging algorithm, faulty circuits, bad solder, etc...and can lead to blowing up your house, etc, in say a worse case scenario.
If its a one celled light (Tk15 with 18650 instead of two 16340, etc), then its more of an issue if the light uses a boost circuit to draw more from the cell, etc.
2) The step down is dramatic on that light, and you might think that high is low after Turbo. So you get ~ 400 lumens on Turbo, for ~ 30 minutes, and then it drops to high, which is ~ 165 lumens. That's a big drop.
If you NEEDED 400 lumens for longer than ~ 30 minutes, then the TK15 is a bad choice, as, that's all its got. You'd need to choose a light that had the ability to SUSTAIN 400 lumens for a few hours, or whatever you DID need...not one that could only hit it for a while on Turbo.
Lights HAVE turbo so you can carry a smaller light, but be able to have the output of a larger more powerful light, for bursts. Its like a runner being able to have a kick, or the ability to sprint for short distances, but, needing to jog the rest of the time.
Now, if you mean its going to low, as in ~ 6 lumens, then its output is dropping down to less than most nightlights put out, and its either malfunctioning or we are back to the cell being bad, etc.
Either way, I'd get rid of the current fake cells and charger, and get real ones that you can be more sure won't blow up and hurt yourself or loved ones.
If the light IS dropping to the low (6 lumens) instead of the high (165 L) from the Turbo (400 L)...then the new cells might "fix" it, or, the light's broken...and you can typically get it repaired under warranty.
If its dropping to 165 L though, that's normal, for the TK15.
If that's a problem for you, because that's not enough light, then you'd want a more powerful light that has a HIGH of 400 L for example, instead of a TURBO of 400 L....assuming you were happy with the 400 L.
400-600 L or so is about all you can GET on extended run time with an 18650, as the math just uses up the cell at that output...the way the gas in your tank is used up faster if you drive floored all the time.
But, you might be able to get a light that pumps out ~ 500 - 600 L on high, with a TURBO mode hitting ~ 950 - 1050 L, etc.
