A single charge per box makes sense, but it might be better to make cake charges smaller and create more of them. I think this might be an enjoyment recipe as opposed to a sustenance recipe, so it makes sense to be able to spread out the morale gain over time by eating your cake a slice at a time.
Also: welcome to the forums Kanto. I see you a lot on the subreddit, it’s good that you’re here too now.