Do you mean you are buying a new CMOS battery every 15 days or so????
WHat PSU, RAM and CPU do you have?
I had replaced the battery four times. now i am skipping the error message and using the pc. the intel dq35jo mother board fitted with intel c2d E8400 processor and 2 gb ram 320GB hdd. power supply type is SMPS but i dont know the make.
I have the DP43TF motherboard. For a couple of years I had no problem with it running on the original CMOS battery. Then one day I noticed the time and date were way off. I had Windows update the time/date. Then, next day I noticed it was off again, and the machine had remained on in the meantime. One day, while using the system I actually saw the time in the lower-left corner change before my eyes. It just flipped - can't remember if it went into future or pas time. But it was apparent it didn't have to be restarted to change time. I replaced the CMOS battery 4 times and every time the battery seemed to last a couple of hours, then the time machine started doing it's thing. Next I'm going to see if replacing the power supply makes any differnece and clean out the case and look for possible shorts.
Do you have effective security and anti-virus/firewall software? The next time such things happen unplug your connection to the internet and see if strange things continue. It sounds to me like your computer is being compromised.
If the PC remains on and the clock is seen to be changing onscreen, this is NOT associated with failure of the coin cell battery on the motherboard.