This invention provides a thermal energy battery having an insulated tank containing a multitude of densely packed plastic tubes filled with a phase-change material (PCM, such as ice) that changes from solid to liquid and vice-versa. Energy is stored when the PCM transitions from liquid to solid form, and released when the PCM transitions back from solid to liquid form. The tubes are arranged vertically, span the height of a well-insulated tank, and are immersed in heat transfer fluid (HTF) contained within the tank. The HTF is an aqueous solution with a freezing point temperature below the freezing point temperature of the chosen PCM. The HTF remains in liquid form at all times during the operation of the battery. Diffusers located allow the HTF to be extracted uniformly from the tank, pumped and cooled by a liquid chiller situated outside the tank and then and inserted back into the tank.