Electricity can change the internal energy of a capacitor or a battery or a piezo electric crystal. The increase in internal energy increases the mass slightly by the equation E= mc2. Since c is large the fluctuation is negligible. That's why the whole idea depends on applying an external force right at the time of the mass fluctuation. This is also contentious because the thrust so developed would be almost immeasurable. Therefore, many scientists suspect that Dr. Woodward is seeing artefacts due to some other source.