Earth batteries are one of the oldest techniques in electroculture’s history — buried pairs of dissimilar metal rods (commonly copper and zinc, or copper and iron) that generate a small, continuous DC current from ordinary soil moisture and mineral content, without any external power source. Electric Fertilizer’s own early experiments used this approach as a low-cost way to apply sustained low-voltage stimulation to soil and root zones.
Because earth batteries rely on real electrode corrosion to generate current, output voltage and current tend to drop as the electrodes degrade, and metal choice matters both for performance and for any long-term buildup of corrosion products in the soil — a genuine open question this page does not claim to resolve. Modern Electric Fertilizer products use external, regulated DC power supplies rather than earth batteries specifically, but the underlying soil-electrochemistry principle is the same one used throughout the site’s mechanism explanations.