@JohnRennie I was thinking about what we were talking about today. All clear, but one thing doesn't come back to me. You actually spoke of two spheres from which the pump drew to transfer charges from one sphere to another.
In the case I described today, however, the situation is slightly different:
In fact, if you think that the metal cable first touches the part of the battery with 0V and then the one with 9V, in fact we can think that the battery how much charge it absorbs, so much it releases.