Ok, dissenting geek opinion here (after all Dan, I am your go-to geek)
Your CMOS battery on your computer works exactly like your car battery. When the car is off, any electrical device you use in the car is run off of battery. So, if you're sitting there listening to your stereo with your lights on, eventually you will run the battery down.
But if you're driving the charging system keeps everything running, and doesn't drain the battery down (in fact it constantly is charging it).
You CMOS battery is good for maintaining your computers 'settings' when your system is turned off. While your system is on, the clock is run off the of AC power from your outlet.
If you left a computer off for a really extended period of time, that battery would run out. So if it's not CMOS, what is it?
So what does it mean? It could mean your computer is running fine and just has trouble with the time, and you just need to live with it. (see below about 'online time')
Or it could be indicative of a general system failure at some point in the future. The problem is it could run like this forever, or it may stop working tomorrow.
If this was a new PC and still under warranty, I would ask for it to be repaired. If this is an older machine, I would make sure I'm doing faithful backups of your important data, and hope it doesn't go on you.
Dan talked about online time syncing - that's a service that runs on your machine that updates your time if it gets off. There are many of them out there, like
http://www.worldtimeserver.com/atomic-clock/
Sorry I can't give you a better answer....