Quick battery drain has two different causes, and confusing them is expensive. First — a worn battery: it physically holds less energy, and no setting will fix that. Second — software: an app running in the background, or a service that keeps the phone awake. You can check this in five minutes in Settings itself.
Check this first
- Settings → Battery → Battery Health. Maximum capacity below 80% means the battery has reached the end of its lifespan. This is Apple's official threshold, not our assessment.
- Settings → Battery, the section with apps. If one app consumed 40–60% in a day — the issue is with it, not the battery.
- Notification about slowdown. When iOS limits performance so the phone doesn't shut down, it tells you about it right in that same section.
Signs the issue is actually the battery
- The phone shuts down at 20–30% and only comes back to life on the charger.
- Battery drops in jumps: was 60%, a minute later 30%.
- In cold weather, the device shuts down almost instantly.
- The housing or screen have lifted — the battery has swelled. This won't "wait until spring": a swollen battery pushes on the display from inside and can crack it.
What calibration does
A full cycle (discharge until shutdown, charge to 100% and leave on charger for another hour) doesn't restore capacity — it only corrects the reading if iOS started showing wrong percentages. The difference is significant: calibration makes sense when the phone shuts down at 40% but Battery Health shows 95%.
What reduces consumption without repair
Auto brightness, dark theme on OLED screens, disabled background refresh for apps you don't use daily, and disabled "Always" location services where "While Using" is enough. This gives you several hours per day — but won't restore capacity below 80%.
When to replace
When capacity is below 80%, when the phone shuts down at live percentages, or when the housing has swelled. Details on thresholds — in the article when it's time to replace iPhone battery. Replacement takes about an hour; you can book a repair for any day.