Mobile applications, such as marine and vehicle, require watertight power devices for use outdoors. However, power devices over 1 KW generate a significant amount of heat from their electrical components, and heat dissipation is made more difficult by the watertight properties. Heat sinks, which are typically effective for thermal management, are not enough to dissipate the amount of heat contained within a watertight package. If the power device cannot sufficiently dissipate the heat, the electrical components will fail due to thermal stress. The design goal here is to provide a watertight Inverter Charger Combination System, which provides up to 2.5 KW of power, with a useful operational temperature range (e.g., −40° C. to +50° C.) through efficient thermal management.