mwatkins

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.

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.

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.