Toshiba Tecra S2 - Manual (Page 121)

TECRA A3/S2 6-4
Power System
Real Time Clock battery
The Real Time Clock (RTC) battery provides power for the internal real time
clock and calendar. It also maintains the system configuration.
If the RTC battery becomes completely discharged, the system loses this
data and the real time clock and calendar stop working. The following
message appears when you turn on the power:
When this error appears, the following action is recommended.
1. Plug in AC over 24 hours
2. Press F2 to enter BIOS setup menu
3. Set correct time and date
S ERROR 0271:Check date and time settings.
WARNING 0251:System CMOS checksum bad - Default
configuration used.
Press <F1> to resume, <F2> to Setup
The computer's RTC battery is a lithium ion battery and should be replaced
only by your dealer or by a TOSHIBA service representative. The battery
can explode if not properly replaced, used, handled or disposed of. Dispose
of the battery as required by local ordinances or regulations.
If you still see error message after above action, please get contact with
TOSHIBA service.