A battery pack includes a battery pack housing having a lid joined to an open end via a fluid-impermeable seal. The battery pack further includes a battery module disposed within the battery housing and comprising a plurality of electrochemical cells. In addition, the battery pack includes a pressure compensation device positioned within the battery pack housing, the pressure compensation device having a first bladder fluidly coupled to a second bladder by a primary fitting. The battery pack housing is filled with a dielectric fluid. And further, the pressure compensation device has a second fluid.