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Keep in mind that the low temp ratings are typically relevant to new cells, and decreases along the same lines as cycle life.
An example is my NiMH smart charger for honda and toyota NiMH packs. Has an option for low temp charging at temps below 40 F. Not recommended to use that option in the chargers manual iirc, but I wouldn't use it after seeing the graphics of how the older weaker cycled packs perform both on the bench and in the car.

 

Impressive study. Done in space and at -20C. No sign of degradation.

"The results showed that the battery can still operate properly at temperatures as low as -20°C. However a reduction of the capacity at low temperatures was observed: The battery's capacity at -20°C was 62% lower than the one at 20°C. The battery fully recovered its capacity after returning back to the nominal working range (20°C), and its performance barely changed thorough the whole range of temperatures studied."

"We can also see, that the performance of the battery (charge/discharge capacity) barely changes and it almost remains constant thorough the whole range of temperatures studied. The changes are also only temporary and the battery is fully recovered after it is put back to the nominal temperature range."

https://upcommons.upc.edu/bitstream/handle/2099.1/26410/David_Balaguer.pdf?sequence=1&isAllowed=y

Battery was charged at -20C and had no negative affects.

 

"For further analysis of the LiFePo4 battery we should also measure capacity and performance but considering the variable number of cycles. With this we could be able to see how affected is the battery when performing hundreds of cycles and in what way do the charge and
discharge cycles change. This analysis however would be destructive, it would require several batteries and it would take much more time."

They only had a single battery. Thus were unable to do the extended life cycle study. The possible damage from charging at below zero could be slight enough to not show up in the tests they did.

 

6. References​

[1] http://www.trisat.um.si/
[2] Maini, Varsha agrawal (2011). Satellite Technology: Principles and Applications
[3] http://earthobservatory.nasa.gov/
[4] MIT Electric Vehicle Team (2008). A Guide to Understanding Battery Specifications.
[5] http://www.batteryuniversity.com/
[6] Kamal K. Kar, Jitendra K. Pandey, Sravendra K. Rana (2014). Handbook of Polymer Nanocomposites. Processing, Performance and Application: Volume B: Carbon Nanotube Based Polymer Composites
[7] Masaki Yoshio,Ralph J. Brodd,Akiya Kozawa (2009). Lithium-Ion Batteries: Science and Technologies.
[8] NI-DAQ™mx C Reference Help (February 2014)


gives an idea about how quickly battery technology is advancing to date

Battery University Homepage

 

So far this is the best -20C research I have seen on LiFePO4 battery. That means that not enough if any research is done on these battery chemistries at below freezing to conclude anything. Other than "so far so good". Only long term time will tell esp for Nexcell packs. The fact that we have users getting good results below freezing is a good sign. It might take many (many) years before we can make any conclusion.

 

Want a test let me have one I'll put 1000+ miles on it a week. And I'll do logs.

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