Can you remove the CMOS battery from a powered computer?

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?

2 Answers

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)

If you remove & replace cmos battery with the power on you can lay the PC on its side or put some sticky tape on the old & new batteries first (or do both). If you do it this way when you pop the old battery out the tape enables you to hold onto the battery & also stops it from falling onto the board. Same deal with the new battery & once it is in place remove the tape.