Why does my phone battery drain overnight?

When a phone sits in a spot with poor reception, it burns power constantly searching for a stronger signal — so a bad-reception bedroom is a surprisingly common cause of overnight drain. Background app refresh and location-hungry apps also keep working while you sleep.

To narrow it down, open your battery screen and look for a single app dominating usage. Turning on battery saver or airplane mode overnight, and limiting background refresh to the apps that truly need it, will cut most of the loss.

Finally, batteries wear out. After a couple of years a battery simply holds less charge, so an older phone can lose more overnight even when nothing is misbehaving. Your settings may show a battery-health figure worth checking.