I’ll buy that. But I swear its not possible to run a radio on batteries made of coconut shells and seawater
The coconut shells are used to hold mango or papaya juice (the electrolyte). A piece of copper wire and a zinc coated nail can be used as electrodes.
Actually the battery charger made from a row of cocoanut shells and wires and whatever was in them was one of the few things the professor made which could conceivably be done in real life.
Now making a geiger counter out of cocoanuts and bamboo was a bit much even for a show in which you had to suspend reality.
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.