This from the 2006 Hybrid Workshop Manual, the factory service manual:

"The degas bottle {spelling checked}has 2 reservoirs and 2 pressure caps. The front (larger) reservoir and pressure relief cap is part of the engine cooling system. The rear (smaller) reservoir and pressure relief cap is part of the motor electronics system.. The 2 reservoirs are separate and both cooling systems are independent of each other.... The vehicle uses a pump driven cooling system, referred to as the motor electronics cooling system (MECS), to transfer heat generated by the electronically controlled continuously variable transaxle (eCVT) and the hybrid electric vehicle (HEV) DC/DC converter to the atmosphere. The system uses a coolant-to-air radiator design." This system is unrelated to the high-voltage battery cooling system which is a separate A/C system. It has its own evaporator, expansion valve and the like.

2006 FEH 4WD Dark Shadow Gray