Screen brightness, by a wide margin
The display is the largest single consumer on any phone, and brightness is the control with the most impact. Turning off Auto-Brightness and leaving the screen at maximum is the most expensive habit there is.
Settings → Accessibility → Display & Text Size → Auto-Brightness should be on. On an OLED iPhone, Dark Mode genuinely helps too, because black pixels are switched off rather than lit — on the LCD models it makes no difference at all.
Background App Refresh, selectively
Settings → General → Background App Refresh. Rather than turning it off wholesale, go down the list and switch off the apps that have no reason to update in the background — games, shopping apps, anything you open deliberately rather than rely on.
Leave it on for messaging and mail, where you actually want the content ready. Our guide to this setting covers what each app loses.
Location services set correctly
Settings → Privacy & Security → Location Services. Apps set to Always can wake the phone repeatedly; almost all of them work perfectly well on While Using the App. Weather and navigation are the exceptions worth leaving alone.
While you are there, Precise Location can be turned off for apps that only need your general area. It saves power and gives away less.
Mail and notifications
A busy mail account set to Push keeps the connection alive constantly. Settings → Apps → Mail → Mail Accounts → Fetch New Data, set to Fetch every 30 minutes or Manually, is a meaningful saving on a heavy account.
Notifications themselves cost little, but each one that lights the screen costs display time. Turning off notifications for apps you ignore anyway helps more than it sounds.
Low Power Mode as a normal setting
Low Power Mode reduces background activity, mail fetch, visual effects and display refresh rate. It is designed as an emergency measure but there is nothing wrong with leaving it on permanently if you value endurance over the last few percent of responsiveness.
Our Low Power Mode guide covers exactly what it changes and how to have it turn on automatically.
What does not work
Force-quitting apps from the app switcher costs more than it saves, because relaunching from cold is far more expensive than resuming a suspended app. Turning off 5G saves very little on a modern iPhone. Disabling Bluetooth saves almost nothing. So-called battery saver apps cannot access anything that would let them help.
And no setting compensates for a worn battery. If Settings → Battery → Battery Health & Charging reads below 80%, that is the ceiling you are working against — our battery health guide covers what the number means.
Frequently Asked Questions
What is the biggest drain on iPhone battery?
Screen brightness. Leaving Auto-Brightness on and using Dark Mode on an OLED iPhone are the two most effective changes.
Does Dark Mode save battery?
On OLED iPhones yes, because black pixels are switched off. On the older LCD models it makes no difference.
Does closing apps improve battery life?
No. Relaunching an app from cold uses more energy than leaving it suspended in the background.
Is it bad to leave Low Power Mode on all the time?
No. It reduces background activity and visual effects, and there is no harm in running it permanently if you prefer the endurance.