Batteries and other devices heat during operation and must be cooled to optimal temperatures. Our SuCCoR method differs from the previous thermal management systems by keeping batteries and devices continuously immersed in a coolant bath kept in a sealed enclosure at its supercritical fluid (SCF) and/or a neighboring thermodynamic state with superb heat conducting properties. While many previous inventions circulated coolants, and some kept devices sealed in a fluid, our invention differs by its use of SCF coolants with no distinct liquid and gas phases. Such a single-phase coolant prevents abrupt loss of cooling due to “vapor lock” formation. Also, using an outer jacketed vessel and a network of heat conducting pipes containing high thermal conductivity and high heat capacity coolants, and deploying cooling fins will enhance efficiency and accelerate heat removal. Our system avoids complex pumps to circulate the coolants, and is lighter and cheaper.