date/time misbehaviour in windows7

[Bill@W]

The date/time settings on my windows 7x64 pro has started arbitrarily resetting itself, usually forwards, by days and hours.
Any ideas on why this should be so (another almost identical system in next room is unaffected)?

[jim]

During use, or between boots?

If your CMOS battery is dead that can screw with the time/date between boots but I thought that tended to reset to a particular date backwards.

Have you checked your internet time settings?

[Bill@W]

Thanks, Jim.
I think you are right in fingering the CMOS battery; I've just checked system time in the BIOS and it is nearly an hour slow. And yes, the time anomaly was between boots. I'll now replace the CMOS battery.

[Bill@W]

Later follow up: The system with the 'low-voltage' CMOS battery is just 4 years old, an Intel self-build. The reason for the early battery problem seems to be that the system was regularly switched on briefly to check mail, occasionally to check a web-site, and then after shut down powered off at the mains. So the poor old lithium battery was getting no nourishment.
Leaving the system switched on for a day restored the battery, and cured the erratic date-time problem.
Lesson: You are not adding much to global warming by leaving your system shut-down but not disconnected.

[Agent]

Later follow up: The system with the 'low-voltage' CMOS battery is just 4 years old, an Intel self-build. The reason for the early battery problem seems to be that the system was regularly switched on briefly to check mail, occasionally to check a web-site, and then after shut down powered off at the mains. So the poor old lithium battery was getting no nourishment.

The battery isn't recharged by the power from the wall. Once they are depleted, it's time to recycle them.
If you're now leaving the power on at the wall, this is why your issue is solved - it will use the +5v standby voltage from your PSU to keep the clock active as opposed to the battery.

[Bill@W]

Thanks Agent for that. The expertise available on Hexus forums is quite amazing.
I thought I knew my way around a PC but this forum is really humbling!