how fast would it cause the battery to degrade, though?

That's the beauty of it. Just get a new one every two years like every other electronic device and you won't need to worry about that. Subscription plans will be available.

I wish the batteries were modular/interchangeable. You could just pull into a station, remove the spent battery and replace it with a full one, the spent one can then just get recharged and stored at the station for the next user to change out. You could even bring some extra ones in the trunk for a long trip!