Here is how you can supposedly charge a car battery using the earth’s electrical field.
A wooden ladder
A piece of sheet metal that is around, say, 1 square meter in size, maybe smaller
A long metal spike
Set the metal sheet on top of the ladder and the car battery on top of that. Attach the jumper cables to the battery, then one cable to the metal sheet. Attach the other cable to the spike and insert in the ground.
With time the sheet metal – and thus the pole attached to it – will reach the same potential as the earth’s field at the height of the ladder. The other pole is grounded. The difference will be enough to charge the battery.
Does this work? Anyone have first hand experience? I don’t know which pole attaches where because I don’t have any info on the earth’s field, but I am assuming it is on the order of tens-of-volts-per-meter at least. (It would have to be.) I do recall reading something about the earth’s field once in Feynman’s lectures on physics. I’d be interested if someone could provide a link.