Then the RTC on the motherboard is suspect. Since we can't change that, we replace the mainboard.
Yes there are Clock cards made like http://www.beaglesoft.com/clcainstall.htm but the price astounds most folk.
Why not enable the time sync to the internet?
For some months now I have found that every time I switch on my 10-year old Evesham PC (Win ME, Athlon 1.1 Ghz, 512 Mb RAM, 40 Gb hard disk), the clock is wrong (slow), sometimes by a few minutes, sometimes by as much as 9 or 10 hours. However, it keeps perfect time while running. I have changed the CR2032 battery 3 times in 2 months but even a brand new Duracell hasn't solved the problem. There are no other anomalies and the PC is still quite fast and stable.
The only significant occurrence some months ago was the disconnection of the power supply, connection of a new one (for tests) and then reconnection of the original one. This solved a problem of the PC failing to power down. However, I think that the clock problem existed before this.