What happens when the plug comes out?

Memory backup

Settings saved

Light and sound stop

Operating battery

Clock keeps running

Until the battery runs down

Original diagram. A “backup battery” can describe either behavior.

Operating batteries come in several patterns

A charged Hatch Rest+ 2nd gen can keep operating away from its charging base. Hatch publishes up to 12 hours under low brightness and volume, while its support material says most users see about eight hours. Nanit Sound + Light also has a rechargeable operating battery, rated up to eight hours.

ZAZU Sam operates on four AA batteries as an alternative to USB power, but the manufacturer does not publish a runtime. The Core Baby Shark ALM204 has an approximately 12-hour rechargeable battery, though its programmed wake sequence glows and sings rather than offering a silent wake cue.

Rest 2nd gen is a different power design

The Hatch Rest 2nd gen has no internal battery and cannot use the Rest+ charging base. It stops when external power is lost, even though saved routines may remain available once power returns.

Generation names matter here: Rest and Rest+ both use app-controlled, multi-step wake and bedtime routines, but only the plus model in this comparison has operating battery backup. Day-of-week selection is documented for Rest+, not for Rest 2nd gen.

Three no-app clocks preserve data but do not operate

The Light to Rise keeps settings for up to 72 hours without external power, but its light, display, and sounds do not run. MELLA's CR2032 coin cell preserves basic memory settings; the manufacturer does not document it operating the cue light or sound.

The Groclock freezes both its time and saved values when power is lost. After a long outage, its clock is behind by the outage duration and needs correcting before the next clock-time cue can be trusted.

Check the wall adapter as well as the battery

Rest+ 2nd gen includes its charging base and custom cable, while Rest 2nd gen includes its custom cable. MELLA includes a four-foot cable and AC wall adapter. Light to Rise and Groclock include USB cables but do not include wall adapters.

That distinction affects what can be used immediately and what must stay connected, even when two boxes both mention USB power.

Translate outage needs into one clear requirement

  • If the cue must still run without wall power, require documented operation on battery; Rest+ 2nd gen, Nanit Sound + Light, ZAZU Sam, and Core Baby Shark ALM204 meet that power requirement with different runtimes and cue styles.
  • If settings only need to survive a short interruption, Light to Rise documents up to 72 hours of retention.
  • If the clock uses time-of-day schedules, account for whether its time continues or freezes during the outage.
  • Do not count a coin cell or a saved-settings claim as operating battery backup.

Manufacturer references

Material reviewed 2026-09-07. Specifications can vary by generation and region.