Kindle Oasis charging cover

When you attach the cover to the device does it charge right away or is there an option that you have to enable for it to start charging your device? I assume it doesn't work this way and that it will keep charging the Kindle as long as it is attached. Say I leave the cover on for protection for like a month. Wouldn't that harm the battery since it'll be charging for one whole month?? I'm confused as to how exactly the charging cover works.

P.S. I don't have a Kindle Oasis. Only interested.