Understand that the Hybrid battery is 240 Volts, why is there a 12 volt battery?

Most of the car's electrical system runs at 12-volts. It is a separate system from the electric motors and the 240-volt batteries.

The 12 volt battery does the same thing in a hybrid that it does in a non-hybrid. Provides the current to start the car and run the radio, lighting, Nav and all the other systems that use 12v. The hybrid batteries run the HSD system (or Ford's version of it).......Traction motor, Generator, AC compressor, Power steering, brakes.........regen. There is no belt to run the power steering or AC compressor..........it runs electrically.

Close, but (as I understand it) not exactly true. The TCH has no 12 v starter and no 12 v alternator. The large traction motor/generator is used to start the car, using power from the 240 v battery, and charging of the 12 v battery is accomplished purely electrically, again taking power from the 240 v battery.

This brings up one of the great disappointing paradoxes of the TCH that I have (sadly) encountered.

The entire electronic control system for the vehicle is on the 12 v system, including the part that enables the starting process and the part that enables charging of the 12 v system.

So, even though the power to start the ICE is always taken from the 240 v system, and even when the 240 v battery is well charged, if the 12 v battery is dead the car simply won't start. And, even worse, there's no way you can access the immense store of electric energy in the 240 v battery to put even a small charge onto the 12 v battery.

What an unfortunate oversight!!

I wish someone would produce an after-market accessory to enable us to tap just enough energy form the 240 v battery to put sufficient charge on the 12 v battery to turn on the control system so that the car would start.

After the first time I got caught by this, I went out and purchased a portable emergency battery to carry in the trunk. I can keep it charged from either an AC charger in the garage or from the DC (cigarette lighter style) outlet in the car when the system is running, and jump the car's 12 v battery from it when necessary.

Interesting side note: I encountered the unfortunate paradox a second time not long afterward. Jumping the dead 12 v battery this way did require putting on a very big charge - just enough to get the voltage up enough to turn on the electronics. After that the aux battery did not need to supply the power needed to start the car -that power came from the 240 v battery ! (silver lining)

The down-side of this approach is that it takes up some of that precious little trunk space. There was some salvation here in my case because the particular unit I got has a small enough height that I was able to strap it securely into the pass-through space behind the rear passenger seat. When I need to use the pass-through, I can simply unstrap the battery and put it on the trunk floor, or even on the floor in the car. It is totally enclosed in a clean, safe, enclosure with a comfortable handle.