This video shows what the battery fan sounds like. Turn your volume up.https://www.youtube.com/watch?v=7p30lMFfVPI
This is the cooling pump, which you'll hear when charging and sometimes while driving. This circulates liquid coolant through the charger/DC-DC converter, motor inverter, and finally the motor.https://www.youtube.com/watch?v=b-JwaR4GIlE
There is a coolant reservoir under the front hood. This is for the coolant-based cabin heater. This is the reason it takes the heater a minute or two before providing heat. It has to heat up the coolant loop.
There is also a coolant reservoir under the rear motor cover in the hatch. This is the coolant loop for the charger/DC-DC converter, motor drive inverter, and the motor itself. This circulates coolant to a small radiator in the front of the i-MiEV. On hot days, the fan up front may come on. I believe it was mentioned earlier in this thread.
The battery itself is air-cooled only. Active cooling only takes place during quick charging. If your i-MiEV has either the cold weather package or quick charge package (premium package on SE), you have the ductwork going to the battery pack and you'll hear the fan on plugin. There is an easy mod to bypass the car's systems and either heat or cool the battery while driving. I'll post the thread link here unless someone beats me to it.