How do I know the CMOS cell is faioing?

[Geek-9pm]

Well, I could just wait until I get errors.
But I go out my Voltmeter.
It says 2.76 volts.
The data sheet says it starts at 3.0 volts.
So can I use this aged battery? Or should I buy a new one?
And what if the new one does not hit very close to 3.0 volts?
Doing Google searches, I did not find any battery maker tart would say for sure.
What do you think?
Curious minds need to know!   

[BC_Programmer]

2.6 Volts or lower is "Dead" for the purposes of a CMOS Battery because it is below the cut-off for TTL/CMOS logic. You can either replace it now or later.

[Geek-9pm]

Thanks, That sound good.
On this computer it is giving me a low voltage alert about half of the time when I start in the morning.  This computer is a real pain to service the CMOS cell. So I have some hesitation about using a aged cell tact is at 2.76 whee I would like 2.9 or higher. I am going to open it up now and measure the cell inside the box.

[BC_Programmer]

Is it not a coin cell or just a pain to access?

The warning is an indicator- likely designed to trigger when the voltage is approaching the 2.6V cut-off point. It shouldn't have any functional effect until you actually reach that cut-off, but of course the voltage will continue to drop.

I don't think the CMOS nowadays really stores anything critically important for boot-up- it's mostly a few preferences. So whether you want to delay it or not shouldn't have a massive impact on how  you use the system, unless the system is one of those ones that refuses to boot at all with a dead CMOS battery.

[Geek-9pm]

So far it never lost anyt settings. So thealert was prematujre.
The cell is a CR2032 and is hard to get to. have to slide out the hard drive and release a ssmall fan to get to the cell holder. I took out the cell and it have a normal, but low voltage.

But In the process I did something wrong. I saw a lot of dust and sprayed it away. But the spray I was using  contained water. Bad move! It took almost ahalf an hoer for the PC to come back to life. And I had pulled loose the VGA cable, which is the primary monitor. So I took almost an  hour to get back here. I am using my Optiplex 745 Ultra small form PC.
Picture of my dual monitor desktop

Yeah, that little box is the 745 ultra tiny. I have  Windows 10 running on it. And Windows 10 wants me to use the Dvorak keyboard!
This is not my day! 

Moral: Always check the CMOS cell first!