There is a battery about the size of a quarter on most motherboards 
today which provides power to save cmos settings when the computer is 
unplugged.   I think the  standard battery is a CR2016, similar to what 
is used in many remotes for cars today.  There is also a CR2025 and 
CR2032, which are thicker.  (20xx is 20 mm in diameter, xx16/xx25/xx32 
is 1.6, 2.5 or 3.2 mm thick).
Other than throwing off the clock, I've never seen a problem where the 
computer won't boot due to a dead battery.
Paul Hachmeyer

Darcy Lidge wrote:

>I was using a refurbished Pentium III Desktop (no name). During the boot process, I kept getting a message "Warning: Battery low. 2.26V or V 2.26". I went into the BIOS setup and changed the CPU speed to manual. Now the computer will not boot. What happened? Could this be related to the CMOS chip and if not, what battery is the system referring to?
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