As I noted in the thought experiment, this is in physics land
(a place where we can ignore confounding variables to keep these demos simple). I have chosen to ignore Ohm's law, etc. for the purposes of simplicity - I could add in total circuit resistance, etc but will avoid it for now.
If anybody wants to add to this thought experiment, find the current required to run the walkman. Be sure to "set" a resistance value.
More importantly though, how much power is required - this can tell you what the efficiency of running across the earth's surface to power a walkman is in comparison to a battery. This would be a ratio of "Power".