Whenever you feel that your PC is showing you wrong time or date then its not a problem of your PC but a problem of your CMOS Battery which is failed or which is on a very low power level and you need to replace it with a new battery which costs around a dollar. If your PC starts giving these kind of errors CMOS Read Error, CMOS checksum error, or CMOS Battery Failure then its the right time.
You dont need to take your PC to a hardware engineer to replace this because its a big battery located in your CPU which can be easily found and removed. You can buy the battery either online or at any PC hardware store, but make sure its of the same type and size.
Open your CPU and try to find the big battery location on the mother board and remove it, followed by replacing it with the new battery. First Unplug the PC from the power source and make sure, the areas near the processor are cool, then start removing the battery which is a little bit fixed within 2-6 plastic pins just to make sure that the battery does not move while the PC is moved.
You need to keep in mind that during the process of changing the battery you can lost a lot of information like the BIOS passwords and settings. The overall process is real easy but should be processed with care and you need to get a new battery which is the same as the dead one.