Energy storage devices, servers, and methods for controlling the same are disclosed. The energy storage device can include at least one battery pack, a network interface configured to exchange data with a server, and a connector that receives alternating current (AC) power from an internal power network or outputs AC power to the internal power network. Energy storage device can also include a power converter configured to convert the AC power from the internal power network into direct current (DC) power based on the information about the power to store when information about power to store is received from the server, or, convert DC power stored in the battery pack into AC power based on the information about the power to output when information about power to output to the internal power network is received from the server. Accordingly, energy may be more efficiently stored.