The globe is witnessing a significant energy transformation with an increasing proportion of variable energy sources like wind and solar on the grid. Energy storage solutions are required to enable a seamless integration of these renewable energy sources. This paper presents a novel isothermal compressed air energy storage (CAES) consisting of two floating storage vessels in the deep ocean that operates by balancing the pressure of the upper and lower tanks with the oceanic pressure. The methodology consists of estimating the proposed system's energy storage potential and operational parametrization. Results show that the maximum compression ratio between the two storage vessels is four, which significantly increases the system's efficiency and lowers compression costs. Compressed air seesaw energy storage is a cheap alternative for storing compressed air because it does not require large, pressurized tanks or sand cavers. It is expected to cost between 10 and 50 USD/kWh for electric energy storage and between 800 and 1500 USD/kW for the installed power capacity. Seesaw is an interesting alternative to pumped hydro and hydrogen for long-term energy storage cycles in islands and coastal regions close to the deep sea.