A self-contained expandable automatic pressure compensated accumulator system for storing and releasing hydraulic fluid energy for use by subsea equipment having a controller, a pressure source, a bidirectional valve fluidly connected to the pressure source, an expandable multisided vessel fluidly connected to the bidirectional valve having a plurality of axial folds between first and second ends, and a bidirectional port connected to the pressure source. As the plurality of axial folds expand, a contracted volume of pressure expands increasing stored hydraulic fluid energy in the expandable multisided vessel. As the plurality of axial folds contract, the expanded volume reduces, releasing stored hydraulic fluid energy to nearby subsea equipment on demand as changes in hydraulic fluid energy requirements for the subsea equipment changes. Simultaneously, hydrostatic seawater pressure of seawater on the expandable multisided vessel is counteracted with the hydrostatic pressure of fluid inside the expandable multisided vessel.