It’s expected that your phone battery will drain during the day while you use it. The screen is the biggest culprit of battery drain, which is why active use consumes so much more juice.
But why does your battery drop when you’re not even using it, like overnight as you sleep? Your phone performs a lot of tasks that take battery power, even while you’re not using the device. And while some drop is expected, heavy battery decrease could point to other issues you need to fix.
Poor signals
Your phone keeps asking if anyone can hear it
Aside from the screen, the various radios inside your phone are one of its most power-hungry functions. The worst offender is the cellular radio that connects your phone to your mobile carrier’s service.
When you’re on a stable connection, the drain isn’t terrible. However, on a bad connection, your phone keeps searching for a better option, boosting its transmission power. This uses lots of energy, and can result in heavy battery drain in a relatively short time. At the extreme, it’s why using airplane mode is important while flying—your phone can’t keep up with the rapidly changing towers.
5G takes more power than 4G/LTE, and Wi-Fi is more efficient than both. When you’re somewhere with no cellular signal, enable airplane mode or turn off your cellular connection (Settings > Cellular on iPhone, or on Android, Settings > Network & internet > SIMs and disable the toggle for your SIM).
This will prevent your phone from constantly checking for networks when there’s no connection available. Make sure you turn data back on when you leave!
Apps working in the background
They’re going even when you aren’t looking
Even when you aren’t using your device, many apps are working hard. In the background, apps will sync data, check for notifications, update your feeds, and perform other tasks. This means you don’t have to wait for updates upon opening apps, but it can waste a lot of battery for small conveniences.
The best way to control this is by revoking background permissions for apps that don’t need it. First, check to see which apps are using the most battery. On Android, go to Settings > Battery > Battery usage; on iPhone, visit Settings > Battery > View All Battery Usage.
If any apps look suspiciously high (apps you haven’t been actively using), you should turn off background refresh for them. Certain types of apps drain your battery more than others.
We’ve covered how to stop apps from running in the background on Android. For iPhone, visit Settings > General > Background App Refresh. If you need to reduce drain quickly and don’t want to decide on individual apps, turn on your phone’s battery saver mode.
Don’t disable background refreshing for apps that require timely notifications, like messaging apps. Disabling their background access could mean you don’t get alerts on time.
Notifications lighting up the screen
The display needs a lot of power
Earlier, I mentioned the screen being the biggest battery drain culprit. While this might seem like a non-factor while you’re not using your phone, it can still have an effect. By default, every notification wakes up your phone and turns on the display for a few seconds. If you get a lot of alerts, this (plus the vibration for each ping) can add up over time.
An easy fix to reduce this is to put your phone face down when you’re not using it. The iPhone, and many Android phones, will detect when the phone is face down and won’t turn the screen on when notifications arrive.
For a more flexible solution, you should set up your phone’s Focus modes to suppress unwanted notifications. Hiding most notifications while you sleep or work means your phone screen turns on less often, conserving battery.
Finally, I recommend turning off your phone’s always-on display, unless you rely on it. In my experience, keeping the screen on all the time (even in this reduced way) isn’t valuable or worth the battery drain.
Software bugs
Misbehaving apps can use up your battery
Issues happen, whether with the OS itself or apps on your phone. An app might temporarily run in the background more than it’s supposed to, or there might be OS processes that get out of control.
Restarting your phone regularly is one line of defense against these issues. You likely don’t restart your phone as often as your computer, but it’s worth rebooting it at least a few times a month to solve any minor hiccups.
While it’s common advice, installing updates is also important. Sometimes developers push buggy updates that use more battery than they should, then follow up with a patch to resolve it. For example, after I installed iOS 26, my battery life was noticeably worse (for weeks) until I installed iOS 26.1, at which point it went back to normal.
On Android, there’s also a chance that your phone could have malware installed, but this is unlikely unless you’ve sideloaded shady apps. If you’ve ruled everything else out, look through your installed apps list and remove anything you don’t recognize or don’t use anymore.
A worn-out battery
That old battery isn’t what it used to be
Finally, it could be that your phone’s battery health has dropped, so it doesn’t hold as much of a charge as it used to. At 80% battery health, your battery is considered to be “consumed” and should be replaced. This means when your phone says it’s 100% charged, it only holds as much charge as it did at 80% when new.
If you’ve looked into all the other causes and nothing seems to be the culprit, check your phone’s battery health in the Settings > Battery menu. If it’s 80% or lower, and you don’t plan to get a new phone soon, then investing in a battery replacement is wise.
You can cull inactive battery drain
By checking these common causes and using the Battery usage menus featured on both Android and iOS, you can figure out why your phone drains when you aren’t doing anything. It’s normal to drop a few percent every hour as your phone runs everything it needs to, but if your phone drops wildly overnight or while you work, something is wrong.
Speaking of overnight drain, it’s worth running a few tests to narrow down where your issue occurs. Charge your phone to a standard level, then overnight, turn on airplane mode (make sure Wi-Fi and Bluetooth are disabled) and see how much your battery drains. The next night, do the same, but with only Wi-Fi enabled while mobile data stays off. Finalize the test with one more night when you have all radios enabled.
If your battery doesn’t drain with airplane mode on, then your battery and the OS are fine. And if your battery doesn’t drain with Wi-Fi on, then you don’t have a rogue app installed. A poor cell signal is the culprit if you only see drain when mobile data is enabled; turn it off at night to conserve juice.
Sometimes, idle battery drain is a short-term issue. If you’re visiting a friend’s house and have no cell signal in the basement, disabling data and using their Wi-Fi is the best option. If you took a lot of pictures during the day, your phone will work harder overnight to back them up, so you should plug it in that night.
These individual cases have easy fixes, but now you know what to do if the issue is persistent.
