Multi-stack Proton Exchange Membrane (PEM) fuel cell systems have received growing interest owing to their high operation efficiency, larger capacity, and flexible operation mode. One of the biggest hurdles for the application of a multi-stack PEM fuel cell system is its limited durability. A load allocation strategy is proposed based on the deterioration information of a fuel cell system. This allocation strategy aims at extending the system's lifetime through better management of its deterioration. A dynamic type of load demand is considered as the system production requirement. The decision-making process takes the fuel cell resistance of the different stacks as inputs and decides the optimal load allocation for the PEM fuel cell system. In the proposed setting, the load allocation is updated whenever there is a demand change event until system failure. The behavior and performance of the proposed allocation strategy are assessed by Monte Carlo simulations. The lifetime distribution results of the proposed load allocation strategy are compared with the classical average load split method. It is confirmed that the proposed strategy can efficiently balance overall system deterioration, thus achieving an improved lifetime for the studied fuel cell system.