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We have determined the variation of the electrochemical potential difference in a gravitational field, and the results agree to within 4% with the predictions of the Equivalence Principle (EP). Thus, EP has again been verified, but unlike previous experiments, this experiment involved charged particles. The results were obtained using a DC SQUID in which the two junctions were separated vertically by about 7 cms. The junctions, which were phase-locked to an external microwave source, acted as two very precise batteries. Because of the gravitational red-shift of the radiation, a voltage difference of 1:1017existed between these batteries, giving a net EMF in the SQUID loop in the absence of other effects of about 2×10-21volts. The loop EMF determined by the rate of change of flux in the loop was however less than 1×10-22volts, thus demonstrating the additional variation in the potential difference due to the gravitational field.