frozenlead :
Some manufacturers use non-rechargeable batteries for their CMOS batteries, so charging it may not do anything.
Where are you measuring the voltage from? Even if the battery is good, they way it connects to the board may not be.
Hi frozenlead, WR2,
sorry for taking so long to get back to you, I tried a few things meanwhile (including a BIOS-upgrade to the latest version 2.80).
I measured the CMOS-battery voltage directly at the pins respectively at the soldering pads of the mainboard (the RTC-battery is a rechargeable type according to the Toshiba manual). I could not check the conducting paths any further since I got no schematics of the board. But obviously the CMOS-reset is not due to the battery, since the change of the battery brought no solution. I suppose there has to be another fault resulting in the reset. Maybe the operating system (Win XP pro SP3) or some other piece of malicious software interferes with the BIOS-settings (Windows actually has writing access, if I'm right). What substantiates my suspicion is that everything's O.K. when I detach the harddisk. Without the system disk there is no reset, even when I pull out the AC-adapter and the laptop battery in the meantime!
Thank you for your advice!
Cheers!