A vehicle includes a traction battery and a controller. The controller is programmed to output an age value of the traction battery based on a ratio of a reference capacity value to an initial reference capacity. The reference capacity value is derived from a mean and a standard deviation of a plurality of historical battery capacity values and has a predetermined probability of being less than an actual battery capacity. The controller is programmed to adjust a battery control strategy based on the age value. The vehicle includes an instrument cluster that is configured to display the age value.