Moisture degradation is a serious hurdle for the commercialization of perovskite solar cells. Recently, mixed cation perovskites (MCPs) have shown promise in achieving relatively longer stability and consistently higher power conversion efficiency than single cation counterparts. Increased stability is due in part to the large grains created through the use of the mixed cation material, which leads to fewer pathways for the penetration of moisture. Furthermore, it has previously been shown that trapped charges are likely the core origin for degradation of perovskite material. Using MAPbI/Br as control and CsFAMAPbI/Br as the mixed cation perovskite, we measured trap density of states (tDoS) along the grain boundaries through KPFM and capacitance sweeps. These measurements were performed at 0%, 25%, 50%, and 75% relative humidity conditions for comparison. The mixed cation samples showed lower tDoS under moisture exposure, pointing to the reason for prolonged stability. Through this work, we can further understand the degradation pathway of mixed cation perovskite and the effect MA may play in the moisture stability of the device, moving one step closer to the commercialization of perovskite solar cells.