A system employing a modular containerized energy-storage systems (ESS) and power cabinet control system allows for long duration uninterruptible power supply (UPS) capabilities for battery and electrochemical storage devices. modular containerized ESS and power cabinet control system. Long duration uninterruptible power supply (UPS) capabilities for battery and electrochemical storage devices may be realized. Embodiments of a modularized energy storage system can comprise a first power cabinet configured to function as a primary power and load balancing appliance. The first power cabinet can comprises power electronics including a DC-AC inverter, transformer, and frequency regulator; a set of one or more energy storage systems, which may be battery-based.