CMOS resetting after unplugging brick

[SBHack]

after unplugging the cord for a day, the following message appears upon booting system: cmos settings wrong cmos date/time not set
after resetting time and date in setup, all is cool. shouldn't there be a supplemental battery on board to hold this setting in case the main battery discharges? Is it replaceable?

 

[hughva]

Yes, there's a battery and it's replaceable.