# Cold weather AA NiMH performance



## Meku (Oct 8, 2010)

I'm looking for reliable AA NiMH cells for winter climbing and hiking trips. So far the only reliable option has been Energizer L 91 (e2 lithium) batteries but I would like to find rechargeable option. I've heard that Eneloops should handle the cold pretty well but then again I've also heard this only applies to storage and not to the actual usage of the batteries. Is this true? Are there any better options then Eneloops?


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## Lynx_Arc (Oct 8, 2010)

what temps are you going to encounter? I have no clue where you are at to even guess.


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## Meku (Oct 8, 2010)

Anything between 32 F to -31 F (0C to -35C). Extremes are below -40 F (-40C). If it gets bad I go with L 91's but what I'm really looking for is a reliable set of NiMH (or anything that works) in 5 F to -5 range (-15C to -20C) which are the most common winter temperatures I encounter.


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## syncytial (Oct 8, 2010)

This thread may be of interest...


- Syncytial.


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## Meku (Oct 9, 2010)

Thanks for the link. However, these tests seem to be carried out in room temperature with pre-frozen batteries. I'm not sure how these applies to real world conditions since in my experience frozen batteries bounce back relatively fast when exposed to body / warmer temperatures. In practical winter applications I've noticed that most of the time you can find a solutions to store batteries in warmth but when used they are exposed to the cold.

EDIT: Scratch that... It seems the during the measurements the room (freezer) temperature was -22ºC.

EDIT2: Actually the flashlight is in room temperature during measurements so I feel these results actually don't reflect real usage in cold environment.


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## KarlH (Oct 10, 2010)

Sanyo claims good performance from eneloop aa's down to -20C, whatever good performance means. They have 1c discharge curves down to -10C on their web page here: http://www.eneloop.info/home/performance-details/low-temperature.html .

I have tested AccuEvolution D cell lsd nimh inside my freezer at home, which is at 5F give or take a degree. I use them in game camera's and wanted to know if they could handle the cold, and it does not get that cold where I live. I charged 4 in my ICharger 106B+ at 2A rate and let them terminate on delta V. I randomly picked one and put it in the freezer and left it overnight, hooked up my leads the next morning behind the door seal on the freezer and discharged it at 2 amps (.2C for these batteries). When it was done, I discharged the other 3 one at a time at 2 amps and the one that was frozen and discharged in the freezer had just over 90% the capacity of the ones that were not frozen. But those are D cells and I'm sure they can handle cold better than a AA.


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## Black Rose (Oct 10, 2010)

KarlH said:


> Sanyo claims good performance from eneloop aa's down to -20C, whatever good performance means. They have 1c discharge curves down to -10C on their web page here: http://www.eneloop.info/home/performance-details/low-temperature.html .


I am assuming those curves are for the new 1500 charge Eneloops.

I wonder if these discharge curves also apply to the original version of the Eneloops.

EDIT: Never mind, found the info here:



> You need a battery, which is reliable even when having cold temperatures? Before eneloop was suitable for temperatures as low as -10°C - now even until -20°C.


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## Meku (Oct 11, 2010)

Is there any idea how the new 2500 mAh Eneloops will perform in the cold? I've only seen a Sanyo press release about them and it really doesn't tell you much about the actual performance of the product.


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## Obijuan Kenobe (Oct 11, 2010)

I only have experience with this sort of battery while powering radio equipment in the cold. And they sucked. I found I needed to warm the unit to get power to be level and steady. 

But that's a very small sample size, and could be just the particular batteries I have have in my radio.

Maybe I have helped very little with this post.

obi


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## Meku (Oct 11, 2010)

Obijuan Kenobe said:


> I only have experience with this sort of battery while powering radio equipment in the cold. And they sucked. I found I needed to warm the unit to get power to be level and steady.
> 
> But that's a very small sample size, and could be just the particular batteries I have have in my radio.
> 
> ...



In general batteries "suck" when in comes to working in cold. The only (I think) exception are lithium primaries like Energizer L91's. You can comfortably use them in -30C without a problem. I hope the new Eneloop 2500 mAh shows some improvement in that field. However, I still haven't tried the new "1500 cycle" Eneloops in cold conditions so even they sound lot better then other rechargeable solutions.


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## KarlH (Oct 11, 2010)

So I just was looking at 4 eneloops on top of my dresser that have likely been sitting there 2+ months since last charged. I grabbed two and put one in the freezer, both measured 1.326 volts open circuit on my multimeter. Updates on capacity I will edit this post and you will find the results below. I'll discharge one tonight at .5c(1 amp), and the one in the freezer at 5F, I'll discharge while in the freezer tomorrow when I get home from work. These are model HR-3UTG eneloops, not the newer improved ones.

Discharge on the room temperature one is done. It finished at 1637mah. I was trying to remember when they were last charged and I think it was when I gave a friend one of my 2xAA solarforce lights, which was after turkey season and sometime before hot summer weather here. That would make it the May-June timeframe. I will discharge the other one tomorrow after work in the freezer. After 24 hours soaking in the freezer it should be thoroughly frozen


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## Meku (Oct 12, 2010)

KarlH said:


> So I just was looking at 4 eneloops on top of my dresser that have likely been sitting there 2+ months since last charged. I grabbed two and put one in the freezer, both measured 1.326 volts open circuit on my multimeter. Updates on capacity I will edit this post and you will find the results below. I'll discharge one tonight at .5c(1 amp), and the one in the freezer at 5F, I'll discharge while in the freezer tomorrow when I get home from work. These are model HR-3UTG eneloops, not the newer improved ones.
> 
> Discharge on the room temperature one is done. It finished at 1637mah. I was trying to remember when they were last charged and I think it was when I gave a friend one of my 2xAA solarforce lights, which was after turkey season and sometime before hot summer weather here. That would make it the May-June timeframe. I will discharge the other one tomorrow after work in the freezer. After 24 hours soaking in the freezer it should be thoroughly frozen



Cheers for doing the comparison test!


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## KarlH (Oct 12, 2010)

Meku said:


> Cheers for doing the comparison test!


 

Thanks. It is just over 40 minutes into the discharge test inside the freezer. The voltage dropped to 1.07 within 40 seconds discharging at 1 amp according to my ICharger 106b+. Withing 5 minutes or so, the voltage stabilzed at 1.04 and it has been hanging on there so far.


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## KarlH (Oct 12, 2010)

It is finished discharging and my IR thermometer said the freezer temperature was 6.7 F, last time I checked it said 5F. The 24 hour frozen eneloop AA discharged while inside the freezer to 0.9 volts had 1390mah capacity. That is almost 85% of the one I discharged last night at room temperature(1637mah). I'd say at .5C discharge, that is very good performance, especially when sanyo only claims the old eneloops to be good to -10C and my freezer is essentially -20C. In five or so minutes, the at rest open circuit voltage recovered to what is in the picture.


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## tandem (Oct 12, 2010)

That is very impressive. Maybe I don't need to keep lithium primaries for cold weather backups around any more after all.

I wonder how a well used Eneloop holds up, i.e. if low temperatures affect any more or less a cell which has been through a couple hundred cycles already.


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## KarlH (Oct 12, 2010)

I have no idea. My eneloops have at most 10 or 11 cycles on them. Most of those were forming charge to begin with and cycling them at different discharge rates when I first got them.


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## Battery Guy (Oct 12, 2010)

When it comes to low temperature performance for NiMH cells, it is safe to assume that the better the high current performance is, the better the low temperature performance will be.

With that being said, the standard 2000 mAh Eneloop has quite good high current performance, so it does not surprise me that it would perform better at low temperatures than many other NiMH cells. If you want better low temperature performance, you might look to the Elite 1700 AA cells. Although I have not tested them at low temps, it is quite likely the same design features that give them great high current capability would also give them good low temp performance.

So, my advice is to try the standard Eneloops, but keep a spare set of Energizer L91 lithiums on hand. If the Eneloops fail to satisfy, then try a set of Elite 1700 AA cells. Just be aware that the Elite cells have a relatively high self discharge rate, so you need to make sure that you top them off before you need them.

Cheers,
BG


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## HarryN (Oct 13, 2010)

One option to consider is to use a light that runs for many hours on the pack it has at room temperature. As a hypothetical example:
- 3 x AA cells with 2 A-hrs at room temp, - approx 2 hr run time at 1 amp, so it is pulling approx 1/2 C, but probably is close to 2 C at (-40 F).

- 6 x AA cells with 2 A -hrs at room temp - approx 4 hr run time at 1 amp to the LED, but since the draw on the cells is relatively low (about 1/4 C) then it is more likely to support your lower temperature needs.

You might be interested to know that actually VERY FEW led lights have driver electronics that are rated to work at (-40 F), and for good reason - the price for those components is much higher.


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## KarlH (Oct 13, 2010)

Last update, the battery I discharged in the freezer had been sitting at room temperature since last night. I just discharged it to .9 volts so I could charge both up again, and it had a capacity of 241mah. 1390+241= 1631 mah compared to the one I discharged at room temp at 1637 mah. You have to love the consistency of eneloops.


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## ampdude (Oct 13, 2010)

Sounds like a bad cell.

For cold weather I've had okay luck with NIMH and Ni-Cads. Alkalines and Zinc-Chloride/Carbon-Zinc (heavy duty) work okay, but lose a lot of capacity. Lithium AA and CR123A primary cells are the best choice of course.

I think if you're going to use the NIMH in very cold weather I'd stay away from the LSD chemistry and get a set of Powerex or Sanyo 2700's.

I'm curious about the cold weather performance of the NiZn cells ??


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## KarlH (Oct 13, 2010)

ampdude said:


> Sounds like a bad cell.
> [{/QUOTE]
> Ummmm, what sounds like a bad cell? Did you read everything? Those cells had not been charged in a long time, and the one that I discharged tonight at room temp is the same one I discharged to .9v inside my freezer last night, the total capacity matched the control cell. I was just getting the remaining capacity at room temp discharged so I could charge both cells again.


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## ampdude (Oct 13, 2010)

Oh I see. I thought you were saying you only got 241mAh out of the second cell.


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## Meku (Oct 14, 2010)

Thanks KarlH for all the testing and data. If the old Eneloop has performance like this then the new 1500 charge should be a good bet for cold weather use. Even more so, since the yet unreleased Eneloop 2500 is targeted for professional photography one could assume that it has even lower internal resistance then older models and therefore higher performance in cold environment.


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## Battery Guy (Oct 14, 2010)

Meku said:


> Thanks KarlH for all the testing and data. If the old Eneloop has performance like this then the new 1500 charge should be a good bet for cold weather use. Even more so, since the yet unreleased Eneloop 2500 is targeted for professional photography one could assume that it has even lower internal resistance then older models and therefore higher performance in cold environment.



I will be very surprised if the new XX 2500 mAh Eneloops have lower internal resistance than the standard Eneloops. It is extremely hard to design a cell that has both higher capacity AND lower impedance (assuming that the size of the cell is the same...obviously a AA has higher capacity and lower impedance than a AAA, for example). For Sanyo to accomplish this, they would need to have made a significant improvement to the metal hydride alloy or developed a thinner separator, or both. 

I certainly hope that the new XX cells have improved capacity AND lower impedance (and therefore higher power capability), but I would not bet on it.

Cheers,
BG


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## Lynx_Arc (Oct 14, 2010)

Battery Guy said:


> I will be very surprised if the new XX 2500 mAh Eneloops have lower internal resistance than the standard Eneloops. It is extremely hard to design a cell that has both higher capacity AND lower impedance (assuming that the size of the cell is the same...obviously a AA has higher capacity and lower impedance than a AAA, for example). For Sanyo to accomplish this, they would need to have made a significant improvement to the metal hydride alloy or developed a thinner separator, or both.
> 
> I certainly hope that the new XX cells have improved capacity AND lower impedance (and therefore higher power capability), but I would not bet on it.
> 
> ...



I am guessing they are trading internal resistance and self discharge for more capacity so that instead of having 85% capacity after a year they will have 70% or thereabouts after a year perhaps.


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## Meku (Oct 14, 2010)

Lynx_Arc said:


> I am guessing they are trading internal resistance and self discharge for more capacity so that instead of having 85% capacity after a year they will have 70% or thereabouts after a year perhaps.



Wouldn't trading internal resistance on XX be bit counter productive since the product seems to be targeted towards pro photo use? Product with high price tag (the press release had "pro" at least three times so it must be expensive ) higher internal resistance and self discharge with one third of regular eneloops charge cycles wouldn't be much of a hit. My (wild) guess is that they are trading cycles and LSD to achieve higher capacity with lower internal resistance to meet the demands of medium to high power devices.


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## Battery Guy (Oct 14, 2010)

Meku said:


> My (wild) guess is that they are trading cycles and LSD to achieve higher capacity with lower internal resistance to meet the demands of medium to high power devices.



Again, I would be shocked if the new XX 2500 mAh Eneloops have a lower internal resistance than the standard Eneloops. It is extremely difficult to get a 20% increase in capacity and maintain, let alone decrease, internal resistance. 

You might look towards the Powerex 2400 mAh cells for a hint on how I would expect the new Eneloops to perform under high discharge rates. A comparison between the Powerex 2400 and the standard Eneloops can be found here for constant current discharge up to 5 amps. 

That being said, I can't wait to get my hands on these new XX Eneloops! Why oh why are they only being sold in Europe????:mecry:

Cheers,
BG


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