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).

Automatically adjusts to Daylight Savings Time while set the DST on. Atomic Wall Clocks Battery Operated with Alarm - This digital calendar alarm day clock required 3 “AA” long life batteries ...