Weakly nonlinear behavior of electric power transmission through an elastic wall by piezoelectric transducers and acoustic waves near resonance is studied based on the cubic theory of nonlinear electroelasticity. An approximate analytical solution is obtained. Output voltage is calculated and plotted. Basic nonlinear behaviors of the power transmission structure are examined. It is found that near nonlinear resonance the electrical input-output relation loses its linearity, becomes multi-valued, and experiences jumps due to large mechanical deformations. The behavior below and above resonance is qualitatively different and is qualitatively material dependent.