Asked at the counter: “My iPhone battery goes from full to 20% by lunchtime.

A battery is a consumable. Apple’s wording: all rechargeable batteries have a limited lifespan and their capacity and performance decline over time. But fast draining is just as often an app, a setting or a weak signal, and those are free to fix.

FREE, ONE-MINUTE CHECKS

• Open Settings, Battery, Battery Health. Maximum Capacity compares the battery now with when it was new. If you see the message that your battery’s health is significantly degraded and a service provider can replace it, that is your answer: it needs a battery.
• In Settings, Battery, look at the graph and the list below it. If one app is using a large share while you were not using the phone, that app is the problem.

SIMPLE THINGS TO TRY

• Poor signal is a big drain: a phone hunting for signal all day empties fast. If it happens mostly at work or in one building, that is why, and a battery will not fix it.
• Turn off Background App Refresh for apps that do not need it (Settings, General, Background App Refresh) and check Location Services for apps set to Always.
• Lower screen brightness or use Auto-Brightness; the screen is the biggest single drain.
• Update iOS. Battery bugs get fixed in updates.
• Restart the phone once a week if you never switch it off.

WHEN A NEW BATTERY IS THE RIGHT CALL

• Battery Health shows the service message, or Maximum Capacity is around 80% or below and the phone is over two years old.
• The phone shuts down at 20% to 30% on a cold day or under load (a camera or a game).
• The screen is lifting at one edge; a swollen battery pushes the screen out. Stop using the phone and get it looked at; do not press on the screen.

A battery replacement does not affect your data, but back up anyway before any repair.

Sources checked: Apple Support (UK): iPhone battery and performance.