Disclaimer - I am not an expert, but since no one else responded to your post, take the following for what it is worth.
Sounds like you are boiling off water because the battery is getting too hot when connected to the charger. Pull the battery and check the water levels.
If I am not going to ride all winter I pull the battery, make sure it is fully charged, then store it inside. A lot of batteries get fried because of a problem with the tender. My friend had to replace the battery in his BMW GS last spring because his tender fried the battery sometime over the winter. Of course, it is more difficult to remove the battery from his bike since you have to raise the tank. Since it is so easy to pull the battery in the Vstrom, it makes sense to do that over the winter.