Disclosed herein are embodiments of an electrical energy storage unit, a control system, and applications thereof. In an embodiment, the electrical energy storage unit (which may also be referred to as a battery energy storage system (“BESS”) includes a battery system controller and a plurality of battery packs. Each battery pack of the plurality of battery packs has a plurality of battery cells, a battery pack controller that monitors the plurality of battery cells, a battery pack cell balancer that adjusts an amount of energy stored in each battery cell of the plurality of battery cells, and a battery pack charger. The battery pack controller operates the battery pack cell balancer and the battery pack charger to control a state-of-charge of each battery cell of the plurality of battery cells. In an embodiment, the battery cells are lithium ion battery cells.