"... if a device could be made the could run any cell phone from any battery ..."

The answer, broadly speaking, is yes.

Pardon me while I ramble -- this is a topic of great interest to me.

All the phones I've had run on a 3.6 VDC lithium ion or NiMH battery pack.

If you take apart a standard car charger, you will find it's an incredibly simple circuit: it just puts a fuse and a resistor in series, which drop the voltage down to the appropriate level. Mine (for older Nokias) drop 14-ish volts down to about 4.5 volts.

The phone has internal electronics to manage the charge and battery (and optimize its lifespan, etc.).

If you put two AAs in series, to generate 3.1 volts (or 3-AA for 4.5 volts), and had a compatible tip, you should be able to run the phone in an emergency, and put a partial charge on the battery as well. (I'm pretty sure you could improvise a tip with a bit of wire, a bit of foil, some tape, and the tube from the refill of a Bic pen). But: you MUST get the polarity right (normally the centre pin is positive) or risk fatal damage to the phone and/or phone battery.

I'm pretty sure you could attach the same setup directly to the battery pack in an emergency, though this may untimately shorten the lifespan of the rechargeable battery. I have successfully charged them "raw" from a solar panel. But this kind of unregulated charge is tricky -- one went "pop" on me because I left it charging too long.

Other batteries may also be useful energy sources -- such as the 3.6V lithium ions in PDAs, laptops, portable DVD players, etc.

I think the "single AA" chargers must use a "puck" -- that is, a voltage doubler. This is the same kind of circuitry used in LED flashlights that run a LED on two 1.5V alkalines (the LED needs perhaps 3.6 - 4.0 V to run).

I a genuine emergency, where the phone is dead and you have nothing to lose, consider this: if I understand correctly, a phone that's off and close to dead still "pings" local towers, and that can be used to help locate you. You may or may not want to jeopardize that feature by messing with the phone. But if you're sure you have reception, and a few calls will get you out in a hurry, that may be an acceptable risk.

Personally, I wouldn't hesistate to do this. BUT: BIG DISCLAIMER: don't try this unless you accept the risk of damaging the phone and/or battery, and voiding your warranty.

Hope this dog's breakfast of ideas is useful.