Dell Precision T5400 (Late 2007) - Manual (Page 177)

Adding and Replacing Parts 177
The battery may need replacing if you have repeatedly reset the time and date
information after turning on the computer or if one of the following messages
appear:
Time-of-day not set - please run SETUP program
or
Invalid configuration information -
please run SETUP program
or
Strike the F1 key to continue,
F2 to run the setup utility
To determine whether you need to replace the battery, re-enter the time and
date in system setup and exit the program to save the information. Turn off
your computer and disconnect it from the electrical outlet for a few hours;
then reconnect the computer, turn it on, and enter the system setup program
(see "System Setup" on page 89). If the date and time are not correct in
system setup, replace the battery.
You can operate your computer without a battery; however, without a battery,
the configuration information is erased if the computer is turned off or
unplugged from the electrical outlet. In this case, you must enter the system
setup program (see "System Setup" on page 89) and reset the configuration
options.
Replacing the Battery
1 If you have not already done so, write down the configuration information
found in system setup (see "System Setup" on page 89).
2 Follow the procedures in "Before You Begin" on page 151.
3 Remove the computer cover (see "Removing the Computer Cover" on
page 153).
4 Locate the battery socket (see "System Board Components" on page 28).
5 If necessary, disconnect any cables that block access to the battery socket.