Sounds like your motherboard battery is dying or dead... you're not using
your machine enough... the onboard battery(which powers the eprom BIOS
settings) normally trickle charges while your machine is switched on.
Incorrect. If the battery was going, it would cause much more chaos
than just screwing up time settings. CMOS would forget everything on
power-down, causing the machine to dump into BIOS setup on every
restart.
The battery also is not "trickle-charged" while the computer is on.
They are non-rechargable batteries that have no load placed onto them
while the computer power supply is supplying current. Remember: if
you use Start/shutdown, or press the Power button on computer produced
within the last few years, you are NOT turning the computer completely
off. The power supply is still providing a small amount of power to
the MB for various reasons - and this also saves that battery. The
battery isn't getting a charge in either case - it's just not being
used.