Mirko Parthey composed on 2017-01-17 00:36 (UTC+0100):
The BIOS clock could still have the correct time despite a dead battery because the Linux system gets the time from an NTP server and writes it to the BIOS clock on shutdown. The clock then runs on ATX standby power and will only lose its memory when the power cable is removed. The same applies to the BIOS settings.
That's the logical expectation, but not the way it always works. Just hours ago on a Dell SFF Optiplex 745 I found a dead battery. After installing a new one I decided to remove it after first setting the BIOS clock and rebooting. Without having removed the power cable, only removing the battery and no other changes, on first subsequent boot it reported BIOS settings reset, and sure enough, clock was reset to its build date just short of 10 years ago.
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