Yes, the two AA batteries provide the 3 volts for backup. But looking at the service manual brought up another interesting item.
The micro-controller in that unit (IC-202) has input pin that checks the system voltages. It says in the manual for pin 20:
"Battery 4 V check input terminal. Monitors in intervals of 100uS. If low for 3 consecutive times a flashing "E" is displayed and 7 seconds later the power is switched off."
The circuit that drives this pin is a comparator that checks the 6 volts and the 3 volts. As long as they are within limits the comparator output is in range and the "4 V" check is satisfied. It is possible that one of the diodes, or even the electrolytic capacitor in the comparison circuit are bad. If you can read a schematic, and have a volt meter, the circuitry could be checked. I would double check the batteries and make sure their contacts in the battery compartment is good.
I read through the section that describes the controls, but I didn't find anything that referenced a master reset. The micro-controller (IC-202) does have a reset pin but that is controlled by a electrolytic capacitor charging through a resistor. That means the micro-controller is reset every time you turn the unit on.
I looked at the schematic and didn't see any hidden reset. However, sometimes they use a special key sequence to trigger a complete reset operation.
As far as the download, I have have no problems. That same Service Manual is also available at:
mods.dk -> Instruction, users and service manuals for Panasonic
but to get the manual on that site, you need to generate a login. I can put either one of those manuals on my own web site and send you a link, if you like.