Bistable piezoelectric energy harvesters are prominent solutions in the field of vibration energy harvesting due to their broadband behavior. However, the impact of the electrical interface and especially the load impedance needs to be addressed. In this study, the impact of the electrical load resistance on the dynamic of the bistable piezoelectric energy harvester has been studied. Through a parametric study, the present paper shows that the load resistance impacts both the harvested power and the bandwidth of the harvester. The analytical expression of the mass displacement, critical angular frequency and harvested power have been obtained, based on a truncated harmonic balance method. A comparison between the analytical model and experimental measurement on a custom bistable energy harvester is then presented. The experimental results are in good agreement with the analytical model, which proves the validity of the proposed model and analysis. The results presented in this study should be considered in the development of maximum power point tracking algorithms and orbit jump strategies.