Since I store most of my old, but working hardware - "you never know, if there come the day, you may have a use for it" - I made the experience of empty CMOS batteries a few times.
As long as your time and date are not set to weird values again everytime you repower your machine, the battery is OK.
If not it's just annoying, but it ain't no serious issue. Set time and date correctly everytime by hand when you repower your machine, until you replace the battery - if the machine really is continued to be actually used in that case.
It depends on a whole bunch of factors, but those batteries are meant for the computer's lifetime, and normally last at least app. ~fifteen to twenty years.
It's a rare situation the CMOS battery becomes depleted on a machine still in use. If so, just replace it, and you're good to go for another fifteen to twenty years.
The battery is either OK, or NOK. There is no need for the operating system to control its voltage.
IMO such things come from people I call "conky-watchers". You know, those who install conky to continously watch: "My disk is at 11.34% capacity. 14.7% RAM used, swap empty. All eight CPU cores at 2.400 MHz@43°C...
" - but missing: conky itself uses more CPU time than everything else together...
However:
There are two tests to figure out for sure, if the battery is depleted:
1. Take your
multimeter and measure its voltage.
2. After you set the machine's time and date (BIOS setting was enough), power it off. Make it completely powerfree. Since power supply units still powering some parts of a main board while the machine is 'officially' switched off, you need to pull the power chord. (Then hit the power on button. On many boards are LED signalling several things; they all need to be dark.) Or even better (carefully!) pull the main boards power connector. Wait for a couple of minutes (some capacitors may have some charge left.)
Then power your machine on again.
If the time is still correct, the battery is OK.
If time and date are resetted to some weird, ancient date like 00:01am 1.1.1970, or such, the battery is dead.
There are two workarounds:
1. If the battery is not soldered to the board, simply replace it by a new one anyway, so, you don't need to care about it anymore.
Of course, you could also replace a soldered battery, but since I neither know your soldering skills, nor your equipment I will not recommend that. (Never ever get even near some electronics with a soldering gun or some plumber's soldering iron!)
Get the exact fitting battery cell (All you need to know is written on it. The internet helps you on finding a suitable replacement [size and nominal voltage must fit; rest doesn't matter.]) Cost 1..2 bucks.
2. Don't care about it at all.
If I read correctly, it's a server, right? So, it runs 24/7 anyway, right? The battery is only needed to keep CMOS settings (time, date, and other things) while the main board is powerless. As long as the machine is powered, time and date are kept. And I bet you're going to use ntpd to set system's time automatically via net, anyway, right?
So, why bother?
