My guess would be that if you're always losing two hours it thinks you're living in a different time zone, or is somehow losing the correct information when you power down. The motherboard battery is one possibility, but it's more likely that for some reason it has lost the plot on the correct time zone. This might be something like a corrupt digit in the file that remembers your clock settings. The best way to fix that is to make some changes, save them, reboot, then restore the correct values and save them.
Double click on the time (bottom right corner on most Windows displays) to get the calendar and clock setting panel and check your time zone, whether it's set to handle daylight saving time properly, and whether it's automatically updating its clock from the internet on boot up (which I strongly recommend if you always have a live internet connection).
If all of these are right make some changes, save them, and reboot, then set it back to the correct values, save, and reboot again.
Hope this helps.
