The manual says "If you want to store the battery pack, you have to take some measures..."
Before storage, the battery pack must be charged;
Be sure 100% the battery pack is switched off;
Recharge the battery pack every 4 week, even it is not used;
Do not store the battery pack under 10°C (50F) or over 40°C (104F);
Do not store the battery pack in wet atmosphere;
Do not store the battery pack exposed to the sun;
Remove the battery pack if necessary.
note the "if" - I wonder if that is mandatory, highly recommended, or truly optional.
Does anyone leave their bike over the winter in the garage, below 50F, without storing the battery?