Corroded
like batteries in a forgotten boombox.
Not so much stored away as set aside with no reason to use it.
When batteries are left in a device that isn't turned on for a long period of time, potassium hydroxide leaks out of them, mixes with air, moisture, salt and voila - powdery blue crust.
Rendering the batteries not completely useless, but it takes a lot of work to clean them off. It's easier to just buy new ones. And once they've corroded, in my experience, their tendency is to corrode again, each time faster than the last. Like I said, easier to just buy new ones.
Me, however, being someone who has a hard time throwing things away, I tend to clean the batteries over and over. Eventually, as if I did not know this was the order of the world, the laws of chemistry, they lose all power and must be replaced.
Still though, I keep them...in baggies to "dispose of properly". It's really hard to find places to recycle batteries. So I have drawers full of them, nearly unrecognizable, covered in delicate blue dust.