System for managing a build-up of thermal energy

A system 1 for managing build-up of thermal energy in a battery comprises a housing 2 enclosing an internal volume 3, in which one or more batteries 12a-e are arranged; an inlet 10 for fluid to flow into the internal volume; a valve (22, Fig 2) operable to control a flow of fluid through the inlet and into the internal volume; and an outlet 11 for fluid to flow out of the internal volume. In use, when the valve permits fluid to flow through the inlet and into the internal volume, the fluid flows over one or more external surfaces of one or more of the batteries before flowing out of the internal volume through the outlet. The system can be associated with at least one sensor (24, Fig 2), such as a temperature sensor, configured to detect a build-up of thermal energy within the housing. When an increase in temperature is detected, a controller (23, Fig 2) can open the valve to allow coolant fluid to flow into the housing. The fluid is preferably a liquid such as seawater, but may also be air. The system may be provided on a battery-powered vehicle such as a boat or aircraft.