Eneloop AAA batts die in light much faster than alkalines... why?

I've tried googling and browsing forum but never found a good explanation for my issue. I got brand new and relatively recent eneloop (standard not pro) triple A batts. I went to put them into my husky aluminum flashlight. A smaller one, 140 lumens I think. Uses 3 triple A batts. I wanted to do a runtime test between the eneloop and some harbor freight brand alkalines. Used meter to check all eneloop were sitting at 1.35v (just charged from Panasonic branded advanced charger). Alkalines were fresh and unused. I noticed after about 30mins of running the flashlight was fairly warm to touch with eneloop. Even warmer after an hour. Not enough to worry, it's aluminum after all. But still I noted it. Light was still same brightness. After 90minutes light was noticeably weak. Batteries tested at just over 1v each. Tested alkalines and light never got warm....huh? Same brightness. And after 2 and a half hours light was still bright. Tested the alkalines after that time and they still say around 1.3v each, so used but still had life left. Can someone tell me what the explanation is here? I'd prefer to use my rechargeable batts in my lights but I'm Not Sure why light (or it was probably the batts....) got noticeably warm and had much shorter run time. For what it's worth I did rhis test with brand new eneloop I just bought a few weeks back but I retested with 3 year old eneloop cells and got similar results.

The alkalines aren't actually giving you the same brightness as the Eneloops, because their voltage sags more under medium to high loads, but it's not a big enough difference that you notice it initially. And over time, the alkalines dim more quickly as the voltage declines until reaching a load level that is easier for them, while the Eneloops have a more consistent brightness.

Here's a graph of runtime and output comparisons between alkaline disposables, Eneloop rechargeables, and the expensive lithium disposables on one light that has similar performance to what you'd see on a lot of unregulated lights like your Husky.

Note the decline in output for all of them, but most pronounced for the alkaline. Because of the lower output, on the other hand, the alkaline actually runs longer. The loss of brightness is often subtle enough that you don't really notice it until you decide to try replacing the batteries and are surprised at how much brighter the light gets.
Source: http://www.led-resource.com/2012/08/led-lenser-p3-afs-p-review/

I took out my meter again and decided to check initial current draw on high mode (mode I tested). With fresh alkalines current draw was 0.37A (with voltage of 4.65v). With the freshly charged eneloops I have voltage of 4.05v, but initial current draw (and sustained as long as I held meter in place) was more than double. 0.89A. No wonder they died faster and got warm. A lot more current was being drawn. What was odd was I went back and forth between cells to see brightness difference. I don't have any equipment to measure light output but to my eyes the flash light was equally bright or very close with either fresh alkalines or fresh eneloop. After an hour and a half or so the eneloop cells were essentially dead. Light was very dim. But same time with alkalines and light (again to naked eye) looked very close to full brightness (I swapped the used alkalines for fresh to see if I could see difference. I saw one but it wasn't particularly pronounced). I'm assuming as you mentioned the husky flashlights are unregulated. Is this simply how it's going to perform? I'm guessing the way light is made it's perhaps meant to perform best with alkalines? It just sucks it draws so much more current with rechargeable cells with little or no perceived benefit in light output.

Thats how light works. We dont see it in a linear way. It's more logarithmic. So 500 lumen is twice as bright as 1000, well on paper atleast. But it's not a big difference at all when eyeballing the differences between a 500, and a 1000 lumen light. One will draw more than double the Amp than the other, but you will not see it as twice as bright. You might think since the dimmest one is 500, the slighly brighter one might be around 600. But in reality it's 1000. You need around 4x the lumens before your eyeballs think a light is twice as bright. And that is the reason i dont care about those huge lumen monster lights. A single cell 18650 1400 lumen light is more than i usual need. To make it look twice as bright i need ~5600 lumen. And now we are talking about 4X18650 cells in a way bigger light. And i dont like to carry huge lights, huge lights always stays at home in my drawer, and the smaller ones come out to play

I suppose I'll just stick with alkalines with my husky lights then. I prefer using eneloops for everything that takes batts but id rather have 3 to 4hrs of slightly dimmer light vs an hour and a half of slightly brighter light. I guess ill have to look at some lights that take 18650 cells for a better rechargeable solution. In the mean time at least, Amazon sells triple A batts very cheap in large quantities. Lol. I'll probably browse these forums and take a look at what people think are good torches to buy that use 18650 cells.

Theelite1x87 said:

I took out my meter again and decided to check initial current draw on high mode (mode I tested). With fresh alkalines current draw was 0.37A (with voltage of 4.65v). With the freshly charged eneloops I have voltage of 4.05v, but initial current draw (and sustained as long as I held meter in place) was more than double. 0.89A. No wonder they died faster and got warm. A lot more current was being drawn. What was odd was I went back and forth between cells to see brightness difference. I don't have any equipment to measure light output but to my eyes the flash light was equally bright or very close with either fresh alkalines or fresh eneloop. After an hour and a half or so the eneloop cells were essentially dead. Light was very dim. But same time with alkalines and light (again to naked eye) looked very close to full brightness (I swapped the used alkalines for fresh to see if I could see difference. I saw one but it wasn't particularly pronounced). I'm assuming as you mentioned the husky flashlights are unregulated. Is this simply how it's going to perform? I'm guessing the way light is made it's perhaps meant to perform best with alkalines? It just sucks it draws so much more current with rechargeable cells with little or no perceived benefit in light output.

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Sounds like your light may be direct drive and is relying on the higher internal resistance of the alkaline cells to limit the current. The extra current and heat generated by using Eneloops in it may greatly shorten the life of the LED. Eneloops generally perform much better in regulated lights, though you still might not get quite as long of a run time, you will usually get closer to full brightness until the Eneloops are dead compared to alkalines which typically drop in brightness through out the run.

If you have a light meter or light meter phone app, you might be able to get an idea of the difference in brightness by setting the meter down facing up with the light pointing up and bouncing it's beam of off a white ceiling.

I would invest in a better headlamp design preferably one that uses another battery type/format light AA or 18650 based. They do have better 3AAA LED lights with at least linear regulators in them that will have the light output identical (to begin with) for both alkaline and nimh but you will still have the alkalines most likely outperforming the nimh on runtime depending on the drive current level of the light and what level the regulator drops out to direct drive.

One "fix" to increase nimh runtime would be to hack into the light and add a limiting resistor to reduce the current down to optimal levels when using nimh batteries. This would however also reduce similarly the alkaline output levels too. I've added a resistor to a 3AAA 8x5mm LED light once to drop drive levels from 40-60ma/LED to 20-25ma/LED using nimh and dramatically increased runtime plus my LEDs didn't burn out either.

Theelite, When I moved from AA lights to 18650 Li-ion lights (1 and 2 cell), I was blown away by performance, run times, etc, not to mention the greater selection of lights available. I stick with the brand name protected cells and they kick butt. My two favorite lights brands are Malkoff and Fenix. Both have great lights, and I've had the occasion to call both on the phone for customer service related questions/issues, and both were stellar.

Iamlucky13, Good explanation, and graph. I wonder how those performance curves would look for a regulated light, like the Fenix E05, other than flatter in the middle.

Jorn, I agree with you about the large 4 and 8 cell lights getting left in the drawer. Aside from the price of the light, 8 good cells would be around $150. Cost effectiveness drops, but it sure is fun seeing all that light.

JT