Embodiments provide modular and reconfigurable battery energy storage systems (RBESSs) exhibiting improved performance and power management capabilities. A power management system is provided to determine a power configuration for a plurality of power storage modules, each having a power storage device (e.g., a battery). The optimized power configuration balances a power load across active power storage modules (e.g., power storage devices being charged or discharged). The power management system is configured to control each power storage module/device on an individual basis, thereby enabling a greater degree of control and flexibility to achieve optimal balancing across a plurality of separate power storage devices within a power system (e.g., a battery pack).