So I turned on the computer...
 

...or tried to this morning and got nothing. Power button lit up for a second and nothing happened. Nada, zip, zero.

This after I got a message yesterday that I posted in another thread complaining about the OS. I won't pollute that one further, just this one.

When I bought this particular computer, I bought two of them I liked the configuration so much. Got one for my wife too but she's since moved on to a Dell. So, I got her old box out of the garage where it'd been sitting on my work bench waiting for a day such as today.
I decided to open hers up to see how hard it would be to get to the system battery. Not much of a problem as long as you remember to reconnect the HD cable that you moved enough to unplug without knowing it. That mystery solved I went on to my computer.
Put a battery I've had sitting around for I don't know how long, and got another message about the battery possibly being dead. It finally booted on the third or fourth try.
So I guess I should go get some fresh batteries for both boxes.

How do motherboards keep these batteries charged up?
Do they perform a charging function when the computer is running?
These boxes were built in May of 2018 so not all that old relatively speaking compared to some of my other boxes which never needed the system battery to be replaced.

The board runs on 5 volts DC, as most electronics. I'm sure that it charges while booted / running.

Most of the batteries I have see in computers are the 2032 small flat batteries. They are not rechargeable, but the motherboard does not draw power from them when on. Most of those batteries only last 6 or 7 years if you turn off the computer when not using it.

It takes very little "juice" to keep the BOIS active. Most folks replace the computer before that battery ever has a problem. Computers age faster than dogs. So a 10 year old computer is really old and slow and get replaced.

Those batteries are used to keep the clock up to date when the computer is off, and other bios settings. They are not rechargeable, Li primary cells.

Don't spit into the wind............
 

is usually good advice, but here goes. The desktop pc I am using right now is a 10-12 year old Gateway. It has been used virtually everyday since it was new and I have had to do absolutely nothing to it in the way of repairs! Is it lightning fast? No, but it works every time, there is still plenty of room left on the hard drive and the video is good running on a medium sized HP screen. It appears that if you get a "good one" they will last nearly forever. I can't remember what I paid for this pc, but I think it was about $800 or thereabouts. In 2010 that was a fairly big price for a desktop pc. When I do need to replace this computer, I will buy one with a solid state drive to get the lightning fast boot time. Other than that, I can't think of much I would want different from this one!