First, let me say that -all- desktops and laptops have a coin cell like this for CMOS, not just most. I doubt it - this would manifest itself in an error in the BIOS, letting you know it was low. Also, these cells usually take years to discharge, mainly because the CMOS uses your laptop battery for its power, so long as its not entirely dead. With desktops, it can take longer - so long as the power supply is plugged in, and the switch is on the "on" position(even when the PC is off), CMOS is powered off that.