Abstract: An energy storage system is removably coupled to a vehicle and includes a frame, a battery supported on the frame, and a frame alignment system. The frame includes a base configured to rest on a support surface while the frame is uncoupled from the vehicle, and a first mounting feature configured to engage a complementary second mounting feature positioned on the vehicle. The battery is configured to provide power to the vehicle while the energy storage system is coupled to the vehicle. The frame alignment system includes a guide surface configured to engage the second mounting feature as the frame is coupled to the vehicle, the engagement between the guide surface and the second mounting feature facilitating alignment between the first mounting feature and the second mounting feature.