Given the substantial issues of environmental pollution and inconvenience associated with batteries, energy harvesting has become an attractive alternative or supplement, with mechanical energy harvesting by piezoelectrics being a prominent technology. However, piezoelectric energy harvesters cannot meet growing energy demands as a result of their low power density, despite the efforts of numerous researchers to enhance performance. Instead, ferroelectric/ferroelastic switching, with greater flows of charge and energy, may offer a viable alternative. In this respect, ferroelectric/ferroelastic switching is attractive because of the greater energies and charge flows involved. However, the associated nonlinearities and the difficulty of establishing a stable working cycle have prevented significant progress. In this work, a robust ferroelectric energy harvester based on partial ferroelectric switching is explored. The device is of simple construction and achieves a per-cycle energy density of about 1 mJ cm−3, orders of magnitude greater than that of typical piezoelectrics. It is shown that only periodic compressive stress is needed to induce the energy harvesting cycles, yielding promising mechanical attributes that limit fatigue or fracture during cyclic loading. The results show this prototype device operating stably over 1.4 × 107 cycles at 20 Hz frequency, demonstrating promise for practical applications. These methods utilize the non-linear response of ferroelectric materials to generate a power density comparable to triboelectrics, surpassing that of piezoelectrics.