[Utilizer]

...not possible to run a radio on batteries made of coconut shells and seawater

Actually, I recall POWs in WWII used to make crude crystal radios with a tiny bit of wire and an old razor blade as a detector. I would assume as long as you could find a source for even a poor semiconductor or even a piece of crystal on the island (volcanic, no?) and enough dissimilar metals you could build a functional one. Not very efficient, but workable.

[JRandomFreeper]

I have a radio here on my 'love me' desk that uses a chunk of galena for the detector, fine wire wrapped around a toilet paper roll for a coil, and foil from a cigarette pack along with the cellophane for a capacitor. It works.

It was the first functioning receiver I ever built. Having 2 clear channel AM stations nearby helped reception. ;)

/johnny