From the Google:
From past studies, scientists knew that most lithium-ion batteries start flatlining at about minus 4°F . Below this point, they don’t hold as much charge, and they aren’t as good as transferring it—meaning that it’s harder to use them for power. And the colder they go, the worse they perform.
-4° F is -20° C which appears to be the magic number
And I think it’s cold at my place
V3 on the driveway tree