A cooling system for cooling a device (150), e.g. a battery, within a vehicle (100), especially a hybrid electric vehicle, the cooling system comprising: a first cooling subsystem (180) for cooling the device (150) and having a relatively low rate of energy consumption, e.g. an ambient air-based cooling apparatus, a second cooling subsystem (182) for cooling the device (150) and having a relatively high rate of energy consumption, e.g. a refrigeration-based cooling apparatus, evaluation means (190P, 190R) comprising predictive evaluation means (190P) for providing a predictive output responsive to a determination whether a temperature of the device (150) will exceed a first prescribed threshold value within a prescribed period of time, an evaluation output of the evaluation means (190P, 190R) being dependent on at least the predictive output of the predictive evaluation means (190P), assessment means (190A) for providing an assessment output responsive to a determination whether the temperature of the device (150) is lowerable by the first cooling subsystem (180) alone, and control means for selectively controlling actuation of the first cooling subsystem (180) or the second cooling subsystem (182) in dependence on the evaluation output of the evaluation means (190P, 190R) and the assessment output of the assessment means (190A). By use of the combined evaluation methodology to operate the lower-energy cooling subsystem (180) in a pre-emptive manner, before or unless the higher-energy cooling subsystem (182) is actually needed, a more energy efficient system is achieved.