system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What ultimately causes batteries to completely die?

Some batteries that sit in unused electronics for an extended amount of time don’t hold charges anymore. 

So is it better to periodically charge electronics that aren’t used regularly just to keep the battery from losing its useable life? Or is it reasonably just a matter of time before batteries aren’t reasonably usable?
gpt
Batteries are basically a little block of material rusting in order to make electrons move. One that little block of material rusts completely, or at least enough that no more if it can rust, it can't make electrons move anymore. As long as there is any connection between the two ends of the battery, even a bit through the inside of the battery, it's rusting in order to make electrons move along the connection.

Rechargable batteries are different because we can reverse the flow of electrical to reverse the rusting, restoring some of the material to it's original condition. This always it to rust again in the future to supply electricity. But the reversing process isn't perfect, so the amount of material that gets restored decreases with each charging cycle, if only a little bit. If the amount of material available gets small enough it won't be able to push as many electrons as hard as it used to when it rusts, and possibly not enough or hard enough to make the device it's attached to run anymore.