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  1. #1
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    flashlight quickly fades to nothing on fresh batteries (Fenix LD20)

    When I put in fresh batteries to my Fenix LD20, it lasts maybe 5 minutes, and then starts to quickly fade to nothing.

    I probably left the previous batteries in it for too long without using it. Is my flashlight a gonner, or anything that can be done to fix it?

    Thanks!

  2. #2
    `````````````` CaptainCool's Avatar
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    Are you using alkalines? Try rechargeables, they can handle the high current load better.

    The previous batteries part might form some corrosion on the contacts, but that should cause poor contact, not a fast fade.

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    Take the flashlight apart and clean all the contact surfaces with alcohol and a rag. Then as the Captain says, use rechargeable batteries, I have the same 8 batteries I cycle through every week, for almost a year now.

    I have used 'long lasting' Energizer non rechargeable batts, and they die far sooner then rechargeable, even on there 100th recharge cycle.

    Seems like an odd symptom.
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    Senior Member Ziemas's Avatar
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    Sounds like bad batteries. Try some decent recharagbles and see what happens.

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    Bike addict, dreamer AdamDZ's Avatar
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    I use alkaline AAs with my CRE flashlights and they work fine, I suspect bad batteries or some kind of current leak/short that drains the batteries fast. I actually used my 1xAA Romisen RC-G2 as a headlight on my tour and it lasted over 2 hours on 2 alkaline AAs.

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    Yeah, I've been using alkalines. I don't think it's an issue with the batteries, as I've tried a couple different brands of brand new batteries. Note that after it fades to nothing, I can wait a while, and put the same batteries back in and it will start bright again before fading to nothing. I've cleaned the contact points with alcohol.

    I can order some rechargeables if you guys think those will work..

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    Another data point: I just noticed it gets really hot before completely turning off. I don't know hot hot these things typically get, but it is hot enough that it is hard to hold.

  8. #8
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    I don't know anything about what a Fenix LD20 flashlight is, so I did a quick Google search and it looks like it has some on board digital circuitry as well as a high intensity bulb.

    Since you have tried different batteries, and without actually knowing what the specs were on the circuitry (such that you could test impedance), I would say that you have a short somewhere, or the power management circuitry is not functioning properly, and thus unduly draining the batteries.

    Not sure what type of bulb that thing uses, but a short there will also cause high drain.

    Put in a fresh set of batteries, turn it on, and after about 2 minutes, immediately take them out and feel them, most likely they will be warm to the touch. This indicates a high drain situation.

    Not sure what kind of trouble shooting is available for that kind of flashlight, but maybe a call to their tech support department. Warranty, return, or replace I suppose are all options.

    What ever happened to simple flashlights?


    EDIT:

    Two things: 1) I have noticed that you indicate that it is getting hot...that is a sure indication of a short; and 2) Rechargeable batteries wont make a hill of beans difference. Indeed, you may even damage the those expensive rechargeable batteries by drawing them down too fast.
    Last edited by zac; 09-28-10 at 10:58 AM.

  9. #9
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    Okay, thanks Zac and everyone. Looks like I'm in the market for a new light (I'll try the tech support with Fenix first).

  10. #10
    Senior Member tarwheel's Avatar
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    Contact Fenix. I bet they would resolve the problem for you if it's due to a short or circuitry issue.

  11. #11
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    So far no reply from Fenix (service@fenixlight.com) ..

  12. #12
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    Interesting, sounds like Zac is right. I hope that Fenix resolves this quickly.
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  13. #13
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    Your Fenix LD20 will actually run better on rechargeable cells than on primary (disposable common) alkalines. NEVER store alkaline cells in a flashlight (or any device) for a long period of time. They can leak, and will corrode the inner workings of your device.

    Try to find Sanyo Eneloop, or Duracell "Pre-charged" (with white top, not black top) rechargeable cells on sale. They are about the most reliable ones out there, good for hundreds of recharges. These are the so-called "LSD" or low self discharge cells which will hold most of their charge for many months, unlike standard rechargeable cells.

    Eneloop or "Duraloop" (a nickname) cells can put out the higher currents these high output flashlights demand, for longer. They will vastly outperform alkalines you buy at the grocery story. Costco often has them on sale.

    PS: They won't leak under normal circumstances, either.
    PSPS: Your light will thank you for the switch.

  14. #14
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    I didn't read zac's post until this morning, wish I had so I could correct some assertions.

    But first, re the LD20, never, ever, ever, store any alkaline cell in any light or other device for the long term. Alkalines are prone to leakage and the material which leaks is highly corrosive and can easily damage or destroy the device. The heat produced by the device as the cell is depleted may be a sign that you've not removed all/any potential corrosion that made have been caused by storing alkaline cells within it. Was there any obvious evidence of leakage? What did the alkaline cells stored for a long time look like when removed? If you saw any evidence of residue on the cells or in the battery tube, then leakage is the root of your current problem.

    Try to remove the head per this photo and do a good job at cleaning it but do not try to disassemble the head further. You risk destroying it. With a pair of needle nose pliers you can unscrew the tail cap - place the tips of the pliers in the little depressions on the inner ring (see photo) - you may find some corrosion in behind there -- that's where the tail clicky switch is located.

    If you can't bring it back from the dead: Some cell makers offer a warranty against this. If your device has been destroyed and it is a Duracell you can try contacting Duracell - they may repair or replace the device. But in the future, just don't leave alky's in devices. Ever.

    Quote Originally Posted by zac View Post
    I don't know anything about what a Fenix LD20 flashlight is
    A Fenix LD20 is a high-output 2 x AA cell LED lightweight flashlight machined out of aluminum and is made to a high quality standard. A typical Fenix (and comparable) light will last for many years of use without any issues at all. Many cyclists in the know have been using such LED lights for cycling, often in conjunction with a TwoFish "bike block" for mounting to handlebars. The light and lights like it make for a very versatile package... offering far brighter output than any production 1 or 2 AA cell off the shelf bike headlamp.

    These days most such AA powered lights are actually designed with rechargeables in mind because alkalines are such poor performers in comparison.

    Quote Originally Posted by zac View Post
    Rechargeable batteries wont make a hill of beans difference. Indeed, you may even damage the those expensive rechargeable batteries by drawing them down too fast.
    That statement is completely wrong, actually, completely backwards in all respects. Before making such a statement you should get acquainted with the nature of modern flashlights and also learn about the properties of modern NiMH rechargeable batteries.

    NiMH rechargeable cells can easily outperform any alkaline cell you may pick up from the grocery store. NiMH rechargeable cells can push out sustained higher current rates for far longer than any alkaline can, and they can do this without reducing the lifespan of the cell. It all has to do with the nature of the chemistries involved.

    Depending on when the OP bought the LD20 it may be the latest revision, the R4, or not. Regardless, the basic principles of the light haven't changed that much from prior versions - the latest simply ups the ante when it comes to output and runtime. Here's a link to a technical review of the LD10 and LD20 R4 models. I direct your attention to output runtime charts for various battery types - compare output and runtime for Alkaline and NiMH cells.

    You can see the difference between using alkaline and NiMH rechargeable cells in the runtime charts -- notice the well regulated (flat line) output trace for the LD20 on "Turbo" when the light is stuffed with Sanyo Eneloops (a highly regarded low self-discharge NiMH rechargeable... available inexpensively at Costco) cells. Then compare the same output trace on Duracell Alkaline cells. Alkaline cells simply don't have the chemical advantage to deliver the sustained current rates needed by these high output devices.

    (Note the charts linked also provide runtimes for the prior generation, the Q5. Yours may be one of the two or an even earlier generation.)

    There is no comparison: On alkalines the LD20 gets only 40 minutes on "turbo" before dropping to 50% of starting output. On a pair of NiMH rechargeable cells, the same light delivers much flatter output on turbo running at full output for almost the entire 1 hour 27 minutes it takes for output to drop to 50% of starting.

    Better quality NiMH rechargeable cells can be recharged hundreds and hundreds of times and hold their properties throughout their lifespan, making their per-use cost in the pennies -- far cheaper than alkalines. That's an attractive attribute as well for cyclists who regularly ride in the gloom and dark.

    I spend approximately $1.75 CAD per cell for a Sanyo Eneloop (actually a Duracell equivalent) when they are on sale. That cell costs a few cents to recharge and I realistically will get at least 300 - 400 charges out of it (rated for 500). Which is more expensive? The alkaline which costs me say 30 - 40 cents each on sale? Or the rechargeable that costs me at most 5 cents (I'm being pessimistic there... my actual local cost is closer to two cents) per recharge?

    The bottom line: alkalines really have no place in modern lights at all. They can't meet the current demands of modern devices. They are expensive when placed in heavily used devices. They are useful as an emergency power source only, but should never, ever, be left in a light or device for a long period of time because of their tendency to leak over the long run, causing corrosion within the device they are in.

    NiMH cells do not have a tendency to leak and are safe to store in devices for long periods of time.

    To the OP:

    If your runtimes are dramatically shorter than the examples given perhaps you need to re-clean your light's contacts. Candlepowerforums.com could also be a helpful resource to you in that regard.

    If your runtimes feel approximately what is listed in the linked charts and review (bearing in mind you'll probably get less output and shorter runtime if you have an earlier version of the LD20), then there is nothing wrong with your light... you are just running it using the wrong cells.
    Last edited by mwatkins; 10-04-10 at 11:56 AM. Reason: added links to charts, some disassembly notes

  15. #15
    Faster but still slow slowandsteady's Avatar
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    Quote Originally Posted by brbbiking View Post
    Yeah, I've been using alkalines. I don't think it's an issue with the batteries, as I've tried a couple different brands of brand new batteries. Note that after it fades to nothing, I can wait a while, and put the same batteries back in and it will start bright again before fading to nothing. I've cleaned the contact points with alcohol.

    I can order some rechargeables if you guys think those will work..
    Did anyone notice this statement? It isn't draining the batteries at all.
    "Ride lots." -- Eddy Merckx

  16. #16
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    Unless the OP has a control light to test in, the use -- fade -- wait -- use (bright again briefly) cycle could just be the cells recovering a little as they tend to do when given a rest.

    I'm assuming since no that the OP has done all that is required to ensure the Alkaline cells that were stored in the light for a long time didn't leak inside and/or leave corrosion behind. It isn't clear from the OP's post that leaking/corrosion was even detected. If they did leak, there would be some evidence of it. Don't forget to clean all the surfaces including the head contact and the tail cap assembly.

    Assuming the light is clean / never leaked in... the only thing left to diagnose is the cells. Unfortunately if the OP keeps trying alkalines and nothing else, there's really no comparison as the OP is comparing one brand of poor quality power to another. Alkalines are terrible, regardless of brand, period full stop say no more -- for this use.

    That said, it should remain bright with fresh cells for more than 5 minutes.

    If the OP wants to cheaply test the light with some good batteries (i.e. doesn't want to invest in rechargeable cells and charger just for a test), then the OP can buy some Energizer L91 Lithium (non rechargeable) cells. These won't cost an arm and a leg for a test.

    Running through two fresh cells with a stop watch in hand should put the "is the light failing" question to rest once and for all. A properly functioning LD20 (new or old vintage) with Lithium primaries in it (the E91's) should put out a stunningly bright light for over 2 hours... if it is a LD20 R4 then for almost 3 hours.

    By contrast, a fresh Duracell (or Energizer) alkaline cell will start to fade from stunningly bright within about 30 minutes -- output will drop rapidly from there.

    Batteries (cells) do matter.
    Last edited by mwatkins; 10-06-10 at 01:03 PM. Reason: clarification

  17. #17
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    Sorry, I missed these last couple posts for a couple days. To try and answer some of the questions: When I first removed the alkalines that I left in there, there was no sign of corrosion or anything out of the ordinary. I cleaned the contact points with alcohol just to sure.

    The reason I think it's the light and not the batteries, is because prior to the couple months of storage, a fresh set of alkalines (similar to what I'm now attempting to use) would give me about 2 hours of run time.

    But if you think it's still worth a shot in trying some rechargeables (or at least the Energizer L91's) I'll do that.

    (Btw, Fenix never responded, even after 3 attempts.)

  18. #18
    Senior Member Ziemas's Avatar
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    Quote Originally Posted by brbbiking View Post
    Sorry, I missed these last couple posts for a couple days. To try and answer some of the questions: When I first removed the alkalines that I left in there, there was no sign of corrosion or anything out of the ordinary. I cleaned the contact points with alcohol just to sure.

    The reason I think it's the light and not the batteries, is because prior to the couple months of storage, a fresh set of alkalines (similar to what I'm now attempting to use) would give me about 2 hours of run time.

    But if you think it's still worth a shot in trying some rechargeables (or at least the Energizer L91's) I'll do that.

    (Btw, Fenix never responded, even after 3 attempts.)
    I'll also try some rechargeables or lithiums first. If those don't change anything try contacting the dealer where you bought it from, not Fenix, which is based in China.

  19. #19
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    Quote Originally Posted by Ziemas View Post
    I'll also try some rechargeables or lithiums first. If those don't change anything try contacting the dealer where you bought it from, not Fenix, which is based in China.
    Yeah, I'll try the rechargeables.

    I bought it from Amazon, and the option to return is no longer available. So I thought I'd turn to the manufacturer warranty (which is still valid). But I haven't tried going further with Amazon (i.e., contact their customer service, etc).

    (I'm not really upset, as it seems like I might be the one to blame, since I left the alkalines stored in there for a couple months.)

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    Based on the further details and given you were getting quite good runtimes off alkalines, chances are it is something to do with the light. Maybe its worth a shot trying the E91's, but before you spend the money perhaps peek inside the tail cap if you've not already done so.

    If you are at all handy with tools, unscrewing the pressure ring in the tail cap with a pair of needle nose pliers isn't too difficult. Even if you aren't handy, you'll be fine if you go at it with some patience.

    You might find something under there that needs cleaning. There's the retaining ring, a small circuit board with the light's switch mounted, a washer I think and then the tail cap rubber boot.

    To put it back, if I recall correctly, with very gentle even pressure with your pliers in both recesses, twist clockwise until you hear a little "click" - twist 1/8 of a turn more - this to ensure you get it seated in the thread correctly... and then reverse direction (counter clockwise) to tighten the retaining ring until firm.

    If you've cleaned the spring, anything under the tailcap, and the head, and it still won't burn for more than 5 minutes, I'm stumped.

    PS: before taking your tail cap apart, remove it from the light and give it a little shake. Hear any rattle? If so (and even if not... please check the tightness of the ring anyway), tighten the silver retaining ring (counter clockwise) until snug. Don't overdo it. Load up your batteries and now try the light...
    Last edited by mwatkins; 10-07-10 at 12:28 AM. Reason: reminder to check for rattle in tail cap / check ring

  21. #21
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    Thumbs up

    It works!

    I cracked open the tailcap and definitely found a lot of gunk in there. Cleaned off all of the little pieces and put it back together. I ran it for 10 mins with no problems (got a little warm, but seems like the normal amount of warmness). I'll do a longer test later. I guess I should switch to non-alkalines now to avoid any problems?

    Here's some pics, in case anyone's interested:

    flash2..jpgflash1..jpg

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    Thanks mwatkins!

  23. #23
    Senior Member Richard Cranium's Avatar
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    I cracked open the tailcap and definitely found a lot of gunk in there.
    The LD20 is a high quality flashlight. Reading the directions must be beyond difficult for you.

    Gee-sus - I hope you don't drive. And if you do - I hope you live far away.....

  24. #24
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    Quote Originally Posted by Richard Cranium View Post
    The LD20 is a high quality flashlight.
    Agreed. I never said it wasn't.
    Quote Originally Posted by Richard Cranium View Post
    Reading the directions must be beyond difficult for you.
    Why do you think that? I already admitted that it was my fault for leaving alkalines sitting in there for a couple months. I was just trying to find out if I could salvage it.
    Quote Originally Posted by Richard Cranium View Post
    Gee-sus - I hope you don't drive. And if you do - I hope you live far away.....
    You should be able to clearly see my location under my name. Apparently you can't read either.

  25. #25
    Senior Member Ziemas's Avatar
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    Quote Originally Posted by Richard Cranium View Post
    The LD20 is a high quality flashlight. Reading the directions must be beyond difficult for you.

    Gee-sus - I hope you don't drive. And if you do - I hope you live far away.....
    Why are you being a dick?

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