Leo actually offered an analogy between a pump and batteries — I have no recollection of what discussion context led him to that; possibly none at all — he sometimes just comes out with random observations. So, anyway, I ran with it:
Then we started doing all sorts of analogical problems of this sort:
This one’s sort of out of control:
Red is the solar system, blue is the (bohr) atomic model, and green is a eukaryotic cell.