Systems and methods for charging a plurality of battery strings are provided. The individual string current of each of the individual battery strings can be monitored and used to regulate a charging output provided by the charger. For instance, the output voltage of charger can be controlled as part of a closed loop control system based on the individual string current of the battery string under the constraint of an individual string current limit and/or a charging voltage limit. As the charging voltage of the charger increases as a result of the closed loop control based on the individual string current, other battery strings can be coupled to the charger when the charging voltage provided by the charger exceeds a battery string voltage associated with the battery string.