A vehicle includes a traction battery subject to alternating cycling and storage modes and a controller. The controller is programmed to calculate an accumulated degradation for the traction battery based on a degradation profile for the traction battery. The degradation profile defines degradation accumulated over time and may differ based on the mode and temperature. The initial degradation value includes the accumulated degradation for the present mode and at least a portion of the accumulated degradation for the other mode. Degradation is then accumulated according to the degradation profile starting from the initial degradation value. The amount of accumulated degradation from the other mode that is included may vary based on the mode and the accumulated degradation.