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I own an old iPod Classic with original lithium-ion polymer battery and I use it primarily while running. Recently I discovered that when a temperature outside is low, usually below 5 C degrees, the battery goes flat really fast and I mean 10 minutes. It doesn't matter if it is fully charged or not, it always goes down faster than when it is 10 degrees or more outside. I know that the device is 10 years old so it doesn't work as good as when it was new, but I'm curious what is the physical reason of the battery going dead faster when in cold environment. I also noticed similar behavior of my laptop battery. Any idea why is that?

Edit:

Here I found some info:

"Cold temperature increases the internal resistance and diminishes the capacity. Batteries that would provide 100 percent capacity at 27°C (80°F) will typically deliver only 50 percent at –18°C (0°F). The capacity decrease is linear with temperature. The capacity decrease is momentary and the level of decline depends on the battery chemistry."

"The performance of all battery chemistries drops drastically at low temperatures. At –20°C (–4°F) most nickel-, lead- and lithium-based batteries stop functioning."

All Wikipedia can say about battery capacity is:

"The fraction of the stored charge that a battery can deliver depends on multiple factors, including battery chemistry, the rate at which the charge is delivered (current), the required terminal voltage, the storage period, ambient temperature and other factors."

It dosen't say anything about how the capacity depends on the electrolyte's internal resistance.

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  • $\begingroup$ Doesn't this say something about how the capacity depends on internal resistance: "Cold temperature increases the internal resistance and diminishes the capacity."!!?? $\endgroup$
    – Hasan
    May 27, 2014 at 9:18

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It's been a while since I studied chemistry, but if I remember correctly: the charge/discharge cycle of a rechargeable battery involves the (mainly) reversible movement of positive ions from the cathode to the anode. In order to move and generate current, the ions must be released from the anode crystal structure and incorporated in to the cathode. In your case, the ions that are moving are Li+.

I'm hypothesizing that at low temperatures, this process takes longer as the ions possess less kinetic energy. That's not to say they'll never be able to make the move, just that they take a longer time to do so at low temperatures relative to higher temperatures. The current drops as a result of this reduced flow, and can't sustain the operation of your iPod.

Essentially, the dynamic operational range of the battery is reduced - initially the process is fast enough to generate sufficient current, but it drops off more quickly at lower temperatures.

Some cool recent research on battery structures is reported here.

I'll wait for someone with more recent knowledge to correct me!

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While it is relevant that the internal resistance of a battery increases when the temperature decreases, and thus the device wastes more energy, I don't think this is the main thing happening. The resistance of a battery would have to increase a lot before the battery itself is the most significant contribution to the loss of energy in a device.

I often go to the mountains, and so many times I've observed what happens when you take a phone from 20 C, bring it somewhere where the temperature is more like -5C, then bring it back to 20C in one day. And here's the explanation I've come up with to explain my observations.

In some sense this plot explains the whole picture, but probably some explanation is in order. Image taken from here

enter image description here

First let's look at normal temperature behavior - 20 C. As the battery is used up, its voltage output decreases. And this voltage output decreasing is actually how your device measures how well charged the battery is.

But when you cool your device, the voltage output of the battery also decreases. Your device interprets this as the battery having lower charge. In extreme cases, it's probably even true that the device can't operate with the reduced voltage. By the way, I'm not sure what's going on with the voltage dip in the beginning, I don't think all batteries do that.

To prevent user-confusion, the iphone at least doesn't allow the charging % to increase unless the charger is plugged in. So I've often seen my phone die in cold temperatures after having the charge % on the screen rapidly decrease. Then I bring it to somewhere with warmer temperatures and plug it in, and it suddenly turns on and says its 60% full. The battery wasn't actually discharged more because it was cold, it just temporarily had its voltage drop and it recovered when it was warm again.

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A simple way to look at this is to realize that a battery relies on chemical reactions to produce electrical power, and this will naturally yield in a first approximation an exponential dependency of reaction rate on absolute temperature.

This breaks down in the case where the battery is so cold that the electrolyte freezes or so hot that it boils. It also breaks down when you include more messy details of exactly how the conductivity of the electrolyte depends on temperature and how the solubility of the ions in it depend on temperature. This means the answer to your specific question will have to come from someone who knows a lot more than I do about battery electrochemistry!

Now note that since the battery has internal resistance, it will be generating internal heat any time it is producing electrical power, and without anywhere to go, that internal heat will raise the temperature of the battery and thereby increase its output. This complicates the analysis.

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