Again, can't say about the FEH/MMH, but our 2003 Prius and the 2007 Prius of a friend's take hybrid battery cooling airflow in from the passenger cabin, assumption being that if you're cool enough, the hybrid battery will get enough cooling airflow. The 2003 intake is in the center of the window package shelf, exit is in the driver's side rear quarter panel. The 2007 has no rear window package shelf so the intake is on the outside edge of the passenger side rear seat.

I suspect the FEH/MMH will have much the same arrangement.

PS: Does the FEH/MMH owners manual say anything about a need to actually use the A/C? Not even on the hottest summer day?

 

I don't know how the Prius does it. However the FEH has a separate cooling system for the battery that consists of a separate evaporator and fan in the back... freon (okay really R-134) is piped through two tubes all the way from the compressor at the front of the vehicle. The system is independent in that the evaporator in the back can be active when the evaporator in the front (for the cabin) is off... but I'm pretty sure the compressor is shared.

If the prius uses more of a passive cooling system it might be because the prius is light enough that the battery doesn't need the same amount of cooling because it draws less current perhaps?

 

Yes, one compressor... and it runs A LOT more often than most of you realize.
I've monitored the A/C compressor extensively, and even in 50'F ambient outside temperature... in city driving, I heat the battery enough to kick the A/C on.

Accelerating briskly draws about 75 amps from that battery pack, for 10-20 seconds at a time. Stomping on the brakes can shove 100 amps back in.
No wonder something in a sealed package would get hot!!!
-John