BIOS

I recently replaced the motherboard on my laptop because of video chip failure. I found the motherboard in the computer salvage computer community and I received it in a Dell box as if it was a new replacement part. The motherboard appeared new all the connectors where real tight as if nothing had ever been plugged in them. I hired a professional computer repair shop to do the work in replacing the motherboard. When I got the laptop back everything worked expect the BIOS RTC Clock will not keep time when the power adapter is disconnected and the laptop battery is bad. Also the BIOS will not take its default setting when trying to do a reset to default in the BIOS. As long as the power adapter remains plugged in the BIOS will retain its setting and the power button will function as it should. If the power adapter is unplugged then reconnected the laptop will startup even with the lid closed. To resolve these issues I sent the laptop to a professional computer repair shop to have the BIOS battery replaced because getting to the battery requires a complete disassembly of the laptop but that did not resolve the problem. Any information available on this subject would be appreciated.