Because Time Machine maintains an active state on volumes it uses, you may need to disable Time Machine (in System Settings > ...

These were chunky dual-in-line devices containing clock and non-volatile RAM chips, a crystal, and a lithium battery. The battery was good for about a decade, which was fine for most PCs of the ...

[RedruM69] recently ran into a system with a dead Real Time Clock (RTC) module ... and 100 or so bytes of battery backed SRAM (before the days of cheap, plentiful flash memory).