The present disclosure provides a method of selectively charging or discharging a system with multiple battery packs connected in parallel when at least one of the battery packs has a significantly different voltage or states of charge (SOCs) than the other battery packs. The method includes charging or discharging the battery pack(s) with a voltage or state of charge (SOC) farthest from a target value until the voltage(s) or SOC(s) is within a range of another battery pack at which point the battery packs may be connected and charging or discharging can resume for the set of connected packs. This process is repeated until all the battery packs are at a predetermined minimum or maximum voltage or SOC threshold. The present disclosure also provides a method for selectively operating and charging at least one of a plurality of battery packs depending on the respective states of the battery packs.