Power Nap on a Mac: what it does while asleep, and whether to turn it off
Power Nap wakes a sleeping Mac to fetch mail, sync and back up. Ours had it on, and its log showed regular maintenance wakes. How to check it and turn it off.
What does Power Nap do?
While the Mac sleeps, Power Nap lets it wake briefly, with the screen off, to check mail, update calendars and notes, sync iCloud and run Time Machine backups. These are the DarkWakes you see in the power log.
Is Power Nap on?
pmset -g | grep powernapOurs printed powernap 1. The log showed regular maintenance DarkWakes of 5 to 6 seconds; see overnight drain for reading them.
How do I turn it off?
Look in System Settings, Battery, Options, if your Mac shows the option there. Otherwise, or to set battery and adapter separately:
sudo pmset -b powernap 0 # off on battery
sudo pmset -c powernap 1 # keep it on when plugged inWhat do I lose?
Mail and iCloud catch up when you open the lid instead of being ready, and Time Machine backs up only while you are awake. On a Mac plugged in overnight there is little reason to turn it off.
See it live
Free Mac's System tab shows what the Mac is drawing from the adapter and the battery, and ranks what is draining it by energy impact, every second. See also pmset settings.
Related: preventing my Mac from sleeping and Read Mac battery data with ioreg.
Common questions
Does Power Nap drain the battery?
A little. It wakes the Mac briefly for mail, sync and backups. Many short wakes add up overnight.
How do I turn off Power Nap on a Mac?
In Battery settings, Options, where shown, or sudo pmset -b powernap 0 for battery only.
What does Power Nap do on a Mac?
Lets a sleeping Mac check mail, sync iCloud and run Time Machine backups.