NiMH not good in cold?

LEDrock

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I've been noticing reduced usage time in colder temperatures (around 45 degrees) as opposed in warmer weather. Usage time seems to be dropping to about half. I heard somewhere that charging NiMH batteries in colder temperatures reduces the usage time because it doesn't charge as well, but I thought they were supposed to work better than alkalines in the cold when actually used there. But is it true?
 

Mr Happy

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Here is a document from Energizer that contains some useful information: http://data.energizer.com/PDFs/nickelmetalhydride_appman.pdf

It contains this interesting graph:
nimhdischargetemperaturez0.gif


At lower temperatures you will see a capacity decrease as above, but also the discharge voltage will be lower. If you combine both effects, the discharge capacity to the low cut-off voltage will be lower than either effect individually.

However, if you are seeing only half the capacity at 45 degrees (about 10 C) then maybe you have some additional troubles. Are the cells in good condition? Does the light have good regulation?
 

Buck91

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What type of discharge rate are the cells seeing? With my bike lights, the cold would severly affect those using lower quality cells (eg. Energize 2500mAh AA's) put higher end batteries do prety good (eg. my Nite Rider Sol battery pack and Duracell pre-charged).

I'm going to play around with li-ion this winter a bit, but remember to never charge a cold li-ion cell! You will get metallic plating which will eventually result in :poof:
 

LEDrock

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Actually, the question is regarding the batteries (NiMH) in my shaver. My bathroom is colder in the morning due to my turning the heat down at night and closing the bathroom door. In the morning, the temp. in there is quite cold. Here are the details: I normally get about 17 shaves before the "low battery" light comes on in the summer. Now that it's colder, I have been getting only about 8. I then made sure to charge it where it was warmer, but had the same results. Then I moved my shaver into a warmer room prior to using it so the batteries would be warmer during use. That seemed to solve everything! I just remember reading in the past about how charging the batteries in the cold isn't the best for them, but I didn't know that using them in the cold had the same negative results.

Here is a document from Energizer that

contains some useful information: http://data.energizer.com/PDFs/nickelmetalhydride_appman.pdf

It contains this interesting graph:
nimhdischargetemperaturez0.gif


At lower temperatures you will see a capacity decrease as above, but also the discharge voltage will be lower. If you combine both effects, the discharge capacity to the low cut-off voltage will be lower than either effect individually.

However, if you are seeing only half the capacity at 45 degrees (about 10 C) then maybe you have some additional troubles. Are the cells in good condition? Does the light have good regulation?
 

Buck91

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Energizer batteries are of the lower quality?!


Energizer 2500mAh NiMH batts are natorisious for poor performance and high self-discharge rates. I have a couple I use in some lower powered lights and they work fine. But I no longer use them in my nicer lights as they just...well, they tend to suck; especially when the temps dip into the single digits (F).
 

JWP_EE

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Depending on the type of shaver, you may find that the shaver is draining the batteries faster when it is cold. If it has some kind of lubrication on the gears inside and it gets thicker when cold, it will require more energy just to run the shaver.
 

bob_ninja

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Actually, the question is regarding the batteries (NiMH) in my shaver. My bathroom is colder in the morning due to my turning the heat down at night and closing the bathroom door. In the morning, the temp. in there is quite cold. Here are the details: I normally get about 17 shaves before the "low battery" light comes on in the summer.

Using NiMH batteries' full capacity and pushing them close to zero SOC certainly reduces their lifespan. I just recharge mine once per week and never got close to empty.

Now that it's colder, I have been getting only about 8. I then made sure to charge it where it was warmer, but had the same results. Then I moved my shaver into a warmer room prior to using it so the batteries would be warmer during use. That seemed to solve everything! I just remember reading in the past about how charging the batteries in the cold isn't the best for them, but I didn't know that using them in the cold had the same negative results.

If they are old tired cells then they may be more sensitive to colder temps and you would see such drastic decline in performance. Just guessing that you cells are getting close to end of life.
 
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