Most battery advice is guesswork. Your phone already knows what drained it, so start there.
Look at the battery screen
Android: Settings, Battery, then Battery usage. You get every app ranked by how much it used since the last full charge.
iPhone: Settings, Battery, and scroll down. You can switch between the last 24 hours and the last 10 days, and tap Show Activity to see screen time against background time.
Read it properly:
- A lot of usage with a lot of screen time is not a fault. You used it. YouTube at the top after an evening of videos is the system working correctly.
- A lot of usage with almost no screen time is the real signal. That app is working while you are not looking, and that is what to chase.
Deal with the app that is misbehaving
Once you have the culprit:
- Update it, in case the version is simply bad.
- Restrict its background use. Android: Settings, Apps, the app, Battery, then Restricted. iPhone: Settings, General, Background App Refresh, and switch it off for that app.
- Turn off its location permission if it does not genuinely need one. Location running constantly is one of the heaviest things an app can do. Settings, Location, App permissions, and set anything that does not need it to Deny or Only while using.
The changes actually worth making
These are the ones with real effect, in rough order:
- Screen brightness. The screen is the single biggest consumer on any phone. Turn on adaptive brightness and stop keeping it at maximum.
- Screen timeout. Set it to 30 seconds. A screen staying on for two minutes after every glance adds up across a day.
- Dark mode, if your phone has an AMOLED screen, which most mid-range and above now do. Black pixels genuinely draw nothing on those.
- Always-on display, off. It is a constant small drain for something you rarely read.
- Battery saver, on, and set it to switch itself on at 20 percent.
Things that are mostly myths: closing all your apps from the recents view (Android restarts them and it costs more than it saves), and any app claiming to optimise your battery, which is itself another app running in the background.
When the battery itself is worn out
Batteries degrade. After two or three years of daily charging, a phone that once lasted all day lasts until mid-afternoon, and no setting will bring that back.
On an iPhone you can see it: Settings, Battery, Battery Health and Charging. Below about 80 percent maximum capacity, replacement is reasonable.
Android rarely shows this directly. The symptoms are: the phone dies suddenly at 20 or 30 percent, it gets hot while charging, or it lasts well only while plugged in.
A swollen battery is a safety problem, not a convenience one. If the back of the phone is lifting, the screen is being pushed out, or the phone rocks when laid flat, stop using it and take it to a technician.
Charging habits
Modern phones handle charging themselves and you do not need to drain them to zero. If your phone offers optimised or adaptive charging, leave it on. Avoid charging in direct sun or under a pillow, because heat ages a battery faster than anything else you can control.