Can you remove the CMOS battery from a powered computer?

Question

I want to take out the CMOS battery while my machine was working to check how much charge it had left in it and I'm curious whether it's going to whack my CMOS settings.

Does the BIOS chip draw power from the motherboard (power supply) while the computer is up and switches to battery power once it turns off?

Are there any other potential problems that might arise from performing such a manipulation: shorts, hangups, other assorted weirdness?

Solution

In at least one case, and probably most cases, the CMOS is powered from the standby 5V supply.

The battery has an estimated life of three years when the Intel® NUC is not plugged into an AC power source. When the computer is plugged in, the standby current from the power supply extends the life of the battery.

BUT, do you really want to work on it while it is powered? There is of course always chance of a short or other problem. What if you drop the battery taking it out of its holder?

(Source)

Comments

[Admin]

Of course you can, I have done this lots of time on a variety of motherboards and other pieces of electronics with similar setups. What are you trying to accomplish here though, reduce downtime? The battery swap only takes seconds, maybe a few minutes if you have issues or stuff in the way so why take the chance of shorting something out, which is possible although unlikely, just shut it down and swap the battery. Is the battery bad? Because I have seen these last for 10+ years in some cases, this is not a normal maintenance process since the worst case scenario is the loss of BIOS settings.

[Admin]

@acejavelin No, of course it's not a life and death thing. I've just been wanting to troubleshoot an issue(read my comment below) and was curious if it's possible to do this safely.

[Admin]

Then just replace the battery... they are like $1 or so, if it work great, if not you are out a $1.

[Max]

Unfortunately, I do because I've been experiencing the problem of losing some(sometimes all) CMOS settings when powering the computer completely off. And the occurrence is inconsistent-sometimes the data is lost, sometimes it isn't. I generally(almost always) have my computer in stand-by mode, so it's difficult to tell whether it's a drained battery(haven't changed it in at least one and a half years) or something more sinister. I kind of wanted to eliminate the battery as the culprit and maybe "hot swap" it if it went dead.