On Thursday, May 17, 2018 at 5:29:29 AM UTC-7, wrote:
I want to concur with Dan.
I fly out of Minden and we cruise between 15,000 and 17,999. It is COLD at that altitude.
My lead batteries would lose voltage as the temp dropped. After three hours at altitude they were lucky to put out 11 volts. Of course, when the batteries warmed up alter landing they had full voltage.
The LiFePO4 batteries do not seem to affected by cold soak. They work the whole flight at full voltage.

This LiFPO battery shows a significant a temperature dependence of voltage:

https://www.batteryspace.com/prod-specs/9055.pdf

Basically, all chemical reactions are very temperature dependent.

Tom