Non-removable batteries are damaged by cold weather. Bringing it inside keeps it/you safer from theft, cold, and throwing out your back carrying your bike.
I knew that charging under water freezing temperatures could damage the battery, not storage or usage. Could you please share some details? I am evaluating to buy an electric bike, but during winter temperature can get to -20 °C/~0 °F, so it would be helpful to learn more about that.