BIOS Time not set

I have an Inspiron 4150 laptop. The laptop used to shutdown after a few minutes after powering it up. I contacted Dell and they replaced my mainboard with a new one which resolved that issue. On powering up the laptop, the Dell bootup screen shows that the board is for a Dell Latitude. But I am guessing that they use the same mainboards. The thing is if I do not use the laptop for a day, and the battery pack is also not in the laptop for the entire day, the next time I boot up the laptop the time in the BIOS is reset and I have to reset the time in the BIOS. This is starting to get annoying as I almost need to reset my BIOS everytime I boot.

Does anyone have any suggestions? I am thinking that the BIOS battery may either be faulty or weak. Thanks in advance.

Joseph