Everything above -10°C is no problem at all for storage. But it is important to fully switch it off and not use it as long as the battery temp low.
Storing in the cold is better than storing in the warm. The chemical reactions and therefore aging of the battery are slowed down. But don't use the bike when the battery is cold.
50% SOC is ideal for storage. Don't let it sit below 20% or above 80%. High and low SOCs will speed up the aging of the battery. If the SOC drops below 0%, the battery could even be damaged. Very important: Don't charge when the battery temp is low (I would not charge it when below 5°C).
So when storing over winter, charge it to about 60%, fully shut it down and put it in a place not too cold.
