Duracell 1000 LED Flashlight Died After Installing Eneloop Batteries

I have some of those 1000 lumen Duracell-branded LED flashlights that Costco sells.

They eat batteries like there's no tomorrow.. so I got me some Eneloop NiMH batteries and installed them.

Turned on the flashlight. Got one bright flash for a millisecond and then no output. Upon closer inspection, I see the LED chip glowing about the same brightness as those old phosphor dial wristwatches. Thinking it was a battery problem, I put the old alkaline batteries back in and the flashlight still wouldn't work.

In the past, I've run LEDs on benchtop power supplies without a current limit resistor, observing that once you exceed a certain amount of current, the LED is irrecoverably ruined and will only glow dimly after that.

I'm wondering if the Duracell LED flashlights lack proper current limiting and rely on the saggy nature of alkaline batteries to limit current below the destructive level? Obviously, the NiMH can deliver a lot more current and although slightly lower voltage than fresh alkaline batteries, they won't sag as much under load.

Be careful with trying rechargeable batteries with these LED flashlights!

Seems more likely to be reverse voltage or a crap driver. Unless they used a particularly crummy LED, most of the stuff we use around here takes 4A+ to burn, and much more to kill, NiMH aren't going to readily deliver that kind of power.

That was my thinking, but this is the first of dozens of LED flashlights that I own to have a LED just suddenly fail like that.
I'm reluctant to try these batteries in my 1300 lumen LED flashlight now.
The flashlight in question turned on and worked normally with the old batteries just prior to installing the NiMH cells. They were installed correctly, too. No reverse polarity or anything like that. It's baffling as to what would go wrong. Coincidence? Sure doesn't seem like!

If it is a light that uses 4 batteries then there is a good chance that it does take into account the internal resistance of alkaline batteries under heavy current loads and using nimh will generate considerably higher voltage to the LED circuitry. I read an article on another site complaining about burning up a 4C version of the light using AA eneloops in adapters.

Duracell makes money from selling batteries, not flashlights. It doesn't surprise me at all that they would design their lights to require alkaleak batteries. Eneloops can provide too much current if the light is so horribly designed that it doesn't even come with a 0.1 cent resistor to limit current.

WalkIntoTheLight said:

Duracell makes money from selling batteries, not flashlights. It doesn't surprise me at all that they would design their lights to require alkaleak batteries. Eneloops can provide too much current if the light is so horribly designed that it doesn't even come with a 0.1 cent resistor to limit current.

Click to expand...

From what I've read on a few sites Duracell does make some lights, has some lights made for them, and allows third parties to license their name on lights that they don't support via warranty. If this is true of Duracell personally I wouldn't buy any of their lights thinking thinking of their name as anything worthy I would just lump them in the vast market of cheap Chinese (and other foreign made) lights.
Rayovac however seems to stand behind their lights well from my past experience while Energizer I'm unsure of but they seem to make decent quality products.

I kinda remember someone posting about one of these being killed by NiMH's, I think it overheated the LED and burned out.

Lynx_Arc said:

If it is a light that uses 4 batteries then there is a good chance that it does take into account the internal resistance of alkaline batteries under heavy current loads and using nimh will generate considerably higher voltage to the LED circuitry. I read an article on another site complaining about burning up a 4C version of the light using AA eneloops in adapters.

Click to expand...

Yes, exactly what this is, a 4 C cell flashlight. The next few posts pretty much confirm this. I should not use NiMH in any of my other 4 cell Duracell LED flashlights.

mweiss said:

I should not use NiMH in any of my other 4 cell Duracell LED flashlights.

Click to expand...

Actually, you should. When you fry your light, you can throw it out and get something better.

mweiss said:

Yes, exactly what this is, a 4 C cell flashlight. The next few posts pretty much confirm this. I should not use NiMH in any of my other 4 cell Duracell LED flashlights.

Click to expand...

I had a cheap 3AAA 8x5mm LED light long ago that I fried the LEDs in using nimh. I then replaced them and put a resistor in the tail cap so the light had less current going to the LEDs than even with the alkalines and it worked perfectly. In order to be sure nimh work you pretty much need to look at the circuitry to determine if it uses a regulator or is essentially direct drive or resistored. Lights using simple resistors or direct drive have a very good chance of frying the LEDs using rechargeable batteries. I have several cheap 3AAA luxeon lights that have linear regulators in them that work the same with nimh or alkalines.

These flashlights are made of extruded aluminum barrels and I can find no means of disassembling them to inspect the circuit that drives the LED. I have no clue how they were assembled. It's quite the mystery. I have tried unscrewing, but the head just turns and turns and turns, but never unscrews.

mweiss said:

These flashlights are made of extruded aluminum barrels and I can find no means of disassembling them to inspect the circuit that drives the LED. I have no clue how they were assembled. It's quite the mystery. I have tried unscrewing, but the head just turns and turns and turns, but never unscrews.

Click to expand...

Try putting a dummy cell in the mix when using rechargeables and see if that works.

If I could build a dummy cell with a resistor.. although the voltage might be too low with only 3 cells.

mweiss said:

Yes, exactly what this is, a 4 C cell flashlight. The next few posts pretty much confirm this. I should not use NiMH in any of my other 4 cell Duracell LED flashlights.

Click to expand...

Yeah I would recommend not using Eneloops in any flashlight unless the maker lists them as compatible in their manual/instructions. Many flashlights makers only recommend alkaline AA/AAA batteries in their flashlights for a reason.
E.g. Streamlight and LED Lenser specifically state on their website and instructions not to use rechargeable batteries (although I have noticed one LED Lenser light where the instructions do specifically list them as compatible).

mweiss said:

If I could build a dummy cell with a resistor.. although the voltage might be too low with only 3 cells.

Click to expand...

It would depend on the current draw of the light engine. If the current draw is a lot it could be dropping the voltage of the alkalines a bunch from 6v to 4.8v or less and 3 nimh batteries is about 4.2v or so when off the charger so it could be as bright or a little dimmer but hold that level of output better than the C cells can.

LEDs have a pretty sharp threshold or 'knee' where current (and light output) falls off suddenly below a certain voltage. A drop of 0.1V could mean a 50% drop in current and hence light output.