The short answer
A healthy phone loses roughly 1 to 3 percent overnight in good signal. If yours loses 15 percent or more, check Settings, Battery for the app at the top of the overnight period. The usual causes are an app refreshing in the background, poor mobile signal forcing the radio to full power, or a battery below 80 percent health.
Overnight drain is one of the easiest phone problems to diagnose, because the phone keeps a detailed record of exactly what used the battery and when. Most people never look at it and replace the phone instead.
What is normal
Sitting idle on Wi-Fi with good signal, a modern phone should use 1 to 3 percent across eight hours. Five to eight percent is unremarkable if you have notifications arriving. Anything above about 15 percent means something specific is happening, and it is findable.
Find the culprit in the battery screen
iPhone: Settings, Battery. Switch to the Last 10 Days view, then tap the bar for last night. Below it you get the list of apps and their share, and crucially a split between screen-on and background activity. Anything with significant background time overnight is your suspect.
Android: Settings, Battery, then Battery usage. Look for the option to show full device usage, and check the graph for a steep slope during the night. Android also shows Screen time and time spent awake, which is the number that matters here.
The pattern of the graph tells you a lot:
- A smooth, steady slope points at the radio — poor signal, or a constant background connection.
- A staircase with sharp drops points at an app waking periodically.
- One large cliff usually means an app crashed and restarted in a loop, or the phone got hot.
The usual causes
Poor mobile signal
This is the most underrated cause by a distance. When signal is weak, the phone raises transmit power and searches constantly for a better cell, and that costs far more energy than anything on screen. A bedroom at the back of the house with one bar will drain a battery overnight on its own.
The test is simple: one night, turn on aeroplane mode and then re-enable Wi-Fi. If the drain disappears, your signal is the cause. The fix is Wi-Fi Calling, which lets the phone stop chasing the cell tower — on iPhone it is in Settings, Mobile Data, Wi-Fi Calling, and on Android in the network settings.
Background app refresh
Social, news, email and delivery apps refresh on a schedule. A handful are badly behaved and refresh constantly. Restrict them rather than disabling the feature wholesale:
- iPhone: Settings, General, Background App Refresh — switch off individual apps, or set the whole feature to Wi-Fi only.
- Android: Settings, Apps, pick the app, Battery, then Restricted.
Location services
An app set to Always for location is the most expensive permission on the phone. Go through the list and move everything you can to While Using. Weather, shopping and social apps rarely need background location, whatever they claim at install.
A battery that is simply worn
On iPhone, Settings, Battery, Battery Health and Charging shows Maximum Capacity. Below 80 percent, expect faster drain and sudden shutdowns. Android varies by manufacturer; Samsung shows battery status under Device care, Diagnostics. A battery replacement is dramatically cheaper than a new phone and restores original runtime.
A clean sequence to fix it
Read the battery graph for last night
Identify the single app with the most background activity. If one app dominates, force-close it, then update or reinstall it. Apps causing drain are frequently fixed in the next release.
Test the signal theory
Spend one night in aeroplane mode with Wi-Fi on. Compare the drain. If it drops to a few percent, enable Wi-Fi Calling and keep Wi-Fi on overnight permanently.
Audit background refresh and location
Turn off Background App Refresh for everything that does not need it, and change every Always location permission you can to While Using. These two changes alone usually halve overnight drain on a phone with many apps installed.
Check battery health
If maximum capacity is below 80 percent, stop troubleshooting software. The battery is consumed and should be replaced.
Restart the phone, then update the OS
A restart clears a stuck process that no setting will fix. Then install any pending system update — battery drain regressions are common after a major OS release and are usually patched within weeks.
If nothing is obvious, uninstall recent apps
If drain started at a particular point, remove anything installed around then, one at a time, giving each a night. Tedious, but it is definitive when the battery screen is not pointing anywhere.
A phone charging under a pillow spends the night hot, and heat is what actually degrades a battery. A cool bedside table, with the phone out from under anything, measurably extends battery lifespan over the years you own it.
Frequently asked questions
One to three percent over eight hours on Wi-Fi with good signal. Up to eight percent is still reasonable with notifications arriving. Above fifteen percent, something specific is running and the battery screen will show it.How much battery should a phone lose overnight?
Generally no, and habitually swiping apps away can make things slightly worse, because relaunching from cold costs more than leaving them suspended. Restrict background refresh for a specific misbehaving app instead.Does closing apps stop battery drain?
The phone increases transmit power and keeps scanning for a better cell. That is one of the most energy-intensive things it does, and it continues all night whether you are using the phone or not.Why does my battery drain faster in a weak signal area?
It is not dangerous, and optimised charging features limit the harm. The real issue is heat — charging under a pillow or in a thick case at a warm room temperature ages the cell faster than the charging itself does.Is it bad to leave the phone charging all night?
Open the battery screen first. The phone already knows the answer and will tell you in about thirty seconds.
