The 12V battery isn't needed to start the ICE directly. It only energizes the HV relay and the main pack runs the traction motor to start the ICE. Still a good point about always leaving it on a trickle charger. Unless there is a problem, the 12V battery should hold a charge for weeks to months.

 

Doesn't the 12V battery power the KAM in the PCM? I assume that the battrey is a standard size? What's the sense to that if it's only needed to close a relay which doesn't require much power?

 

You're right, I wasn't implying that the 12V battery isn't used for anything other than the relay. I just meant to point out that the 12V battery is NOT used to actually start the ICE.

 

What's the CCA of the battery used in the FEH?

 

Mine is a Motorcraft BXT-96R, 500 CCA. I think it's the stock battery for many Ford vehicles.

 

Why all the CCA if it's not used for starting????

 

It's still used to run all the 12V accessories, and there are more of them on these vehicles than conventional vehicles. The water pump and power steering and power brakes are all electric. The only thing that is direct off the ICE is the AC compressor. The 12V battery is used for all those items instead of starting the ICE. Some of those need power even when the ignition is off and the HV pack is isolated, mainly the power brakes which we hear pumping up as soon as we open the door, and the water pump and radiator fan which can run after the ignition is off if the coolant is still too hot. Hence the need for a beefy 12V battery.

 

The FE has EPS also and like all FWD, a radiator fan. Being more dependent on electric powered units, you'd want a larger than needed battery power!

 

Ford publishes an aftermarket modifiers guide at this URL:

http://www.motorcraftservice.com/VDI...D_complete.pdf

In it you'll find some pages that talk of how to mount things so that they don't interfere with airbag deployment.

 

That is a 2006/2007 model paper. They changed the dash layout for the 2008 and newer model.