PC clock

[pintpot]

My PCs clock is running slow - losing an hour or so per day. I assume that the CMOS battery needs changing. Is there anything in particular one should do when changing the battery, like not having the battery disconnected for a long period? Any advice would be helpful!

Thanks,

pintpot

[simonw]

I did this recently, the only thing that happened to me is that the BIOS settings reset itself.

[Jonessie]

It's quite rare for a battery to go on a motherboard, lithium has a three - five year life span, in fact I don't think I have ever seen one fail in 20 years of building and maintaining computers. the BIOS holds the time when you turn off the computer and then you turn it on again it reinstates the time and corrects itself to the current timestamp. Therefore, if the battery is low on power it will lose time each time you turn your computer on and off again.

OK here is something you can do, make a note of the settings for the BIOS and then unplug your PSU and then take out the battery and leave it for about 2 minutes and then put it back in again, plug in the power lead and then reboot and reconfigure the motherboard again with the settings you had before. set the clock to the current time and set the date.

See what happens.

I just thought of something... the BIOS would have advised you at POST the battery was low on power...? has it been unplugged at all...?

[GSte]

the BIOS would have advised you at POST the battery was low on power...? has it been unplugged at all...?

I've never seen that (as I haven't seen many batteries die either ), but I have seen this happen with the clock losing time and there was no error message, yet it was a battery that needed replacing. They're only cheap OP, and although often fiddly to change, as someone else said, it will just erase your BIOS settings is all, so you'll simply have to reset them.

[nibbler]

How old is the battery?
And if you we're changing it, and you're quick enough you probably won't lose settings... take a not anyway.

[peterb]

<----snip the BIOS holds the time when you turn off the computer and then you turn it on again it reinstates the time and corrects itself to the current timestamp. Therefore, if the battery is low on power it will lose time each time you turn your computer on and off again.----->

For the sake of technical correctness the CMOS contains a real time clock which runs continuosly. However when the computer starts it usually runs a software clock which takes real time from the RTC. The RTC usually contains the CMOS memory which maintains BIOS configuration settings. (On the same vein, the expression "Clear the BIOS" is often incorrectly used to mean "Clear the CMOS" to remove any specific BIOS configuration settings)

The CMOS clock isn't that accurate anyway, but an hour a day is indicative of a low battery. Incidentally, the battery only maintains the clock when the computer is completely disconnected from the mains supply, at other times it is maintained by the standby power rail on the PSU.

While replacing the battery is the long term fix (and it generally isn't difficult in itself, the hard bit is getting to it) you could download an application that will update the real time clock from time servers on the internet. One I have used (although it is very old in the tooth now) is About Time http://www.arachnoid.com/abouttime/ although I believe XP has a built in time server client. There are others.

(As a Linux user that isn't an issue as most Linux distros have an SNTP (Simple Network Time Protocol) clients built in anyway which synchronises system time with an SNTP server during the boot process)

[arthurleung]

Or it is possible that there is a short between your motherboard and the case which leak the power out of the button battery.

[mycarsavw]

Right Click the time in the task bar > Adjust Date/Time > Internet time > put a tick in Automatically syncronize <sic> .... > in the "Server:" box type; clock.isc.org and click "Update Now".

Mine hasn't lost a second in the year or so I've been using the above.