Why Do desktop computers have batteries?

Answer 1

They have batteries so that when the main power is turned off. The motherboard can continue to process the passing of time. Thus allowing the computer's clock to keep running. Otherwise every time you turned on your computer the time would be farther and farther behind real time. Principally to keep the real time clock working, although many computers use battery backed CMOS to store things such as hard disk parameters.

Answer 2

The battery is for the system. It is called CMOS. Which stands for Complementary metal-oxide semiconductor.

All this does is allow the system to remember the time and date in the BIOS.

It does not remember BIOS settings only time and date.

Answer 3

Batteries provide electrical power in the absence of an external power supply. This allows for portable computers such as tablet or laptop computers to be carried about without the constant need of a wired power connection.

Many computers also include a small battery to uphold important configuration data, such as the size and geometry of the hard drives, and other important system configuration data.