The car's ICU is what is programmed. The FOB needs only know what it's next rolling code is (if it even uses rolling codes) and that can be stored on NVRAM (flash?) which doesn't require any power to maintain.
I've pulled batteries from overhead door controllers (rolling code systems) for years and when I put the battery back they work just fine.
I expect nothing different from the TCH's SmartKey FOBs.
Worse case is the FOB reverts to it's initial rolling code which I am sure is permanently hardcoded in the FOB as is it's RFID and the TCH's ICU will honor that if need be.

I can appreciate that it stores the code in the NVRAM, but I am still wondering how it was able to start the car with no battery in it.

As mentioned previously, I pulled the battery out and by touching the Toyota logo side to the start button it beeped and I was able to then push the button and get the car running.

Somehow it has to communicate it (and I would think it would take some kind of battery power) with the car by touching the FOB to the start button.

Can you, schmidtj, or anybody else that knows these things answer this issue? Thanks!

The "touch FOB to the start button" uses RFID technology.
No power required on the FOB for that.
Go here:
http://en.wikipedia.org/wiki/RFID
Pay particular attention to the PASSIVE and also
AUTOMOTIVE technology. The Toyota implementation
is referenced directly.
I REEEEEALY wonder if active RFID is the only sustem
used in day to day SmartKey operation since there
are security issues.
It basically uses the power the
start button emits in the form of an RFID beacon and
echos back a reply encoded with it's unique ID. Each
FOB has a unique RFID associated with it.
I am NOT saying that day to day use of the FOB uses RFID.
It isn't nearly as secure as rolling codes but does work when
there is absolutely no power available onboard the FOB.

Thanks for doing the research for me, schmidtj. I was thinking of putting a piece of cellophane between the battery and the contacts on my second FOB and carrying it inside the car as an emergency back-up.

I was afraid of doing this would cause the FOB to eventually become useless. From what you are saying and per that article you pointed out in Wikipedia, I think I will do just what I had in mind.

I've never felt secure without a spare key somewhere within the car. With the FOB, I thought I was out of luck. But, with the FOB (without the battery connected) inside the car and the detachable key secured outside the car, I will once again have the security of a backup key for emergencies.

Thanks again for the explanations.

This plan now under way ...
Only ...
Can a 'used'/'previously owned' fob be used
- either by reprogramming or authorizing/reauthorizing or whatever?

Nothing I could find either way about this ...