Method and system for testing vehicle battery system

A method to test a battery pack in a vehicle comprises determining the vehicle is driven in electric vehicle and regenerative braking modes with respective output rates continuously for threshold amounts of time. The method includes determining first and second sets of battery voltage values for multiple battery pack components in the battery pack as the vehicle is driven in the electric vehicle mode and the regenerative braking mode, respectively. Each first and second set of battery voltage values includes a value for each battery pack component in the multiple battery pack components. The method includes outputting an indicator regarding a state of the battery pack based on differences in pairs of battery voltage values among the first or second sets of battery voltage values. Each pair of battery voltage values includes a maximum and minimum battery voltage value from each first or second sets of battery voltage values.