When should you replace the CMOS battery?

[yoda313]

I have two computers and I am not sure when I last replaced the battery in either of them. Its not a big deal or a big expense obviously but I'm wondering when I should do it as a matter of precaution.

Also what is lost when you unplug it in the bios setting? Do you just enter bios before replacing and then write down the settings so you can reset them after you install the new battery?

It has been awhile since I've done it so I don't remember what happens with the bios. I don't think I have anything funky in the settings. The only thing might be on the one computer I use hdmi out on my video card so I can use my hdtv as a monitor (nothing fancy, my westinghouse 32" hdtv that is about four or five years old now).

So is it just a matter of going to the store and buying the right number and plugging it in? Are there any backup procedures I can do in the bios before starting?

Thanks.

[jagabo]

The CMOS memory that's backed up by the battery will become corrupt. On the next power up the BIOS will warn you and automatically revert to default or fail-safe settings. Then you restore any custom settings you need.

[yoda313]

The CMOS memory that's backed up by the battery will become corrupt. On the next power up the BIOS will warn you and automatically revert to default or fail-safe settings. Then you restore any custom settings you need.

Ok so its a full reset then. I guess I'll pick the batteries up this weekend to force myself to do it. Better safe then sorry.

I'll also take a peek at the bios to see whats what.

Thanks.

[Nelson37]

If you haven't made any custom BIOS settings, you set the date and time and no other problem.

The batteries last about 8 to 10 years or more. CR 2032 watch battery. $5.00

[johns0]

I would wait for the battery to fail,some computers are still running on the same battery since 2000 that i've seen on my service calls,removing the battery will reset your bios anyways.

[ranchhand]

The easiest way to know when the a new battery is needed is when you notice that the date and time in the system tray start varying wildly and won't hold the settings. If your date settings are steady and correct you don't need to replace the battery.

[gll99]

I don't have custom bios settings but for the past few months one of my computers resets the time and date when I shut it down and close the power switch on the back or unplug it to play with something inside. I already know it's the battery but I've just ignored it. All I do is reset the time and date after boot when it happens. I did forget once and downloaded some files and they ended up with a 5 year old date. I got a 3 pack Lithium for $1.25 at the Dollar store a while back but still haven't bothered to install one even though I had the case open 3 or 4 times since then.

[DarrellS]

I thought my battery was going after daylight savings changed because the clock kept going back an hour every time I reset it but I discovered that it was a setting in Windows that kept changing the time.

Right click on clock > Adjust date/time > Internet Time > Untick "Automatically sync with an Internet time server". The internet time server kept setting the time back an hour.

[yoda313]

Well I don't have any clock issues on either computer.

I'm just thinking it might be time to change them out of habit. Kind of like an oil change I guess. Won't take long for sure.

Thanks everyone.

[jagabo]

I've never bothered to replace a battery before it's failed. The consequences of battery failure aren't catastrophic. You just have to reset the BIOS settings.

[lingyi]

I believe as as long as the PC is plugged in, the battery doesn't drain. Which is why a CMOS battery on a laptop will typically die long before a desktop.

There's a very, very slight possibility that the battery will burst and corrode the contacts. I've seen CMOS batteries that have swelled, but never one that burst. The case is very well sealed.

If you have a custom builit PC or high performance PC, the builder may have set changed / tweaked the BIOS settings for you. Be sure to check the settings before you change the battery.

Change it as little or as often as you like. Just remember to reset the clock and any custom BIOS settings you may have when you do.

[johns0]

You don't need to reset the clock and bios settings before changing a battery,the bios will be set to the default setting after a new battery is installed unless you mean to restore the custom settings after a battery change.

[themaster1]

When should you replace the battery hmm let me think...

When it's somewhere around 1.98Volt. I went as low as 1.5 volts with batteries without much trouble but past that mark the pc will play tricks on you.

you can check the voltage with cpuid HW monitor, 3V is perfect

[fritzi93]

When should you replace the battery hmm let me think...

When it's somewhere around 1.98Volt. I went as low as 1.5 volts with batteries without much trouble but past that mark the pc will play tricks on you.

you can check the voltage with cpuid HW monitor, 3V is perfect

Well, what do you know, I never paid any attention to that reading. I presume it's the VBAT voltage? Mine shows 3.3 volts.

[themaster1]

yep Vbat is what you should pay attention to. 3.3V is the highest voltage

[yoda313]

Thanks everyone. I did buy 2 batteries for both computers yesterday. They were duracell and they were 3v. I haven't installed them yet but half the battle is acquisition. So I'm almost there.