7 signs your phone battery needs replacing (and what it costs)

Phone batteries are consumables. Every charge cycle wears the cell slightly, and after two to three years the wear becomes something you feel: the anxiety-charging at lunchtime, the 30%-to-dead cliff, the phone that won't survive a cold platform wait. None of that means the phone is finished — it means a £40–£70 part is.

Here are the seven signs worth acting on, and the honest economics of acting on them.

The seven signs

One: battery health below 85% (Settings → Battery → Battery Health on iPhone — below 85% most people notice, below 80% iOS may throttle performance to prevent shutdowns). Two: the phone no longer lasts a normal day when it used to. Three: sudden shutdowns with 20–30% showing. Four: dying fast in cold weather. Five: running hot while charging. Six: the percentage jumping erratically. Seven — and this one is urgent — any swelling: a bulging back, a lifting screen, a case that no longer fits.

A swollen battery isn't a wait-and-see fault. Stop charging it, don't press on it, and get it seen quickly — pressure on a swollen cell can wreck the screen and, rarely, become a fire risk. We prioritise swollen-battery bookings; see our battery replacement service.

What replacement costs — and what it buys back

Fixed prices at Optimise: Samsung batteries from £40, iPhone batteries from £60, fitted in around 45 minutes with a 12-month warranty — the full per-model table is on the battery replacement page. Compare that with £400+ for a new mid-range phone, and the battery is the highest-value repair in phones: it restores all-day life and removes any health-related throttling in one go.

The maths only fails on phones that were cheap to begin with — a £50 battery in a £70 handset needs thinking about, and we'll say so rather than take the booking. In that case the better route is usually trading it in against a refurbished phone with a stated battery health figure.

Extending the next battery's life

Heat is the killer, not charging habits. Avoid charging in direct sun or under a pillow, take the case off if it runs hot on a fast charger, and don't obsess over the 80% rules — modern phones manage their own charging far better than folklore suggests. Overnight charging is fine; we covered the myth in detail here.