to cut the story short: there are two symptoms I can observe. First every time I turn my laptop on, the clock resets back to 1/1/2009 12:00 AM. even if I don't disconnect my laptop from a direct power source. and second, while the computer is turned on and I'm working with it, sometimes the clock jumps to a random time in future or past. These jumps can be as small as few minutes or as large as dozens of years! I know the problem is not BIOS battery since I've changed that battery myself, but it didn't help at all. Besides, while the computer is connected to power source battery should be practically useless, right?
Here is the full story: I've got an HP Pavilion-dv6-2020ev laptop. about a month ago, I've tried turning on my laptop, but without any previous alters, it didn't turn on. since I don't have access to any authorized HP care center, I've asked an unauthorized technician to fix it. After about 3 weeks he claimed the laptop was fixed. and he said he had changed "Graphics chip", which I think he either meant south bridge or GPU. I got the laptop back, but I still couldn't turn the laptop on. I've changed the adapter since I've suspected there was with that part. Using the new adapter, I could turn the laptop on. I've got a dual boot Windows/Fedora on my system, and I was shocked when I saw grub countdown timer didn't advance, needless to say, neither windows nor fedora couldn't boot. After fedora checking boot log, I saw OS was complaining about HW_CLOCK. So I went to check what was going on in BIOS and saw the system clock was completely stopped. It was fixed exactly at 1/1/2009 12:00 AM. I've changed the clock to correct local time, and after that, the clock started to move forward. After that, both Windows and Linux had no problem booting, but I noticed a new issue. Every time I turned my laptop on the clock resets back to that mentioned time (I think it's the same year as my laptop was manufactured). even if I change the time directly in BIOS and save/quit BIOS menu, the time is not stored after restart caused by BIOS configuration changes. First I've suspected there is something wrong with BIOS battery, but changing it had no effect at all. so I suspect there is something else wrong with my laptop or (to be precise) its motherboard. Now I'm wondering if you could give me any hints where to look for potential problems.
Side Note: system doesn't seem to forget other BIOS settings which makes it even less probable that the Battery is the problem.