Purpose <p>We present a vibration energy harvesting (VEH) system with a vertically oscillating mass coupled to horizontal springs via rigid linkages. Global dynamics analysis evaluates harvesting efficacy and identifies optimal configurations.</p> Methods <p>Static bifurcation analysis elucidates the underlying principle of the bistable configurations. The extended averaging method quantifies intra-well and cross-well resonances. Runge-Kutta integration and the cell-mapping approach numerically characterize the global dynamics of the bistable VEH system, including concurrent steady states, output histories, and basin topologies.</p> Results and Conclusions <p>Under specific structural and material parameter conditions, geometric tuning of the parameter <i>b</i> (spring-end half spacing) precisely modulates the potential barrier height, transitioning the system from deep-well to shallow-well bistability. Deep-well configurations (achieved at minimal values of parameter <i>b</i>) exhibit rare and hidden cross-well steady states, trapped within severely eroded basins of attraction that demand impractical initial-condition precision within the safe basin. Conversely, shallow-well designs eliminate concerns regarding such safe-basin constraints. While a submaximal<i>b</i> design provides marginally greater and more dependable output during high-intensity base vibrations, the maximal <i>b</i> setup manifests outstanding adaptability to low-frequency ambient vibrations, a wider environmentally relevant frequency spectrum, and sustained stable output under low-to-medium vibration amplitudes. The outcomes guide excitation-adaptive customization of VEH systems to maximize efficiency in low-frequency operational regimes.</p>