Phone batteries do not usually fail on one exact birthday. They wear gradually, which is why it can be difficult to decide whether poor battery life is normal ageing, a software problem or a battery that is ready to be replaced.
These seven signs are more useful when you look at them together rather than treating one symptom as proof.
1. The battery drains much faster than it used to
The most obvious sign is a large drop in useful runtime.
Think about the same type of day six or twelve months ago. If the phone once lasted from morning until evening but now needs two or three top-ups without a major change in your use, battery ageing becomes a stronger possibility.
Before replacing it, check Battery settings. A single app using an unusual amount of power can imitate a worn battery.
2. The phone shuts down with charge remaining
Unexpected shutdowns at 20%, 30% or another apparently healthy percentage can point to a battery that can no longer supply power reliably under load.
Cold weather can also temporarily reduce battery performance, and software problems can cause restarts, so repeated shutdowns are more meaningful than a one-off event.
If the shutdowns continue, have the phone checked.
3. The percentage jumps or behaves unpredictably
A battery indicator that falls from 40% to 15% very quickly, gets stuck at one number for a long time or changes sharply after a restart can indicate inaccurate state-of-charge reporting or battery deterioration.
Calibration is not a magic fix for a physically worn cell. If the behaviour is persistent, diagnosis is more useful than repeatedly draining the phone to zero.
4. Battery health shows significant degradation or a service warning
Many modern phones provide battery information in Settings.
On supported iPhones, Apple shows maximum capacity and performance information. Apple describes lithium-ion batteries as consumable components that hold less charge as they chemically age.
A lower maximum-capacity figure should be considered alongside actual use. A phone that still comfortably lasts through your day may not need immediate replacement just because the number has fallen.
Conversely, a phone with serious shutdowns or swelling needs attention even if you have not checked a percentage.
5. Normal tasks cause unusually poor battery life
A worn battery may become obvious during tasks that demand more power, such as navigation, video, camera use or gaming.
But these tasks naturally use more energy, so compare like with like. If the phone suddenly performs much worse doing the same job than it did before, and Battery settings do not reveal a clear app problem, the battery deserves closer inspection.
6. The phone is unusually hot during light use or charging
Some warmth during charging, gaming or software updates is normal. Persistent excessive heat during simple tasks is not something to ignore.
Heat can have many causes, including apps, charging accessories, poor signal and hardware faults. Apple also notes that high temperatures can affect battery lifespan and that iPhone may slow or pause charging when temperatures are outside its preferred range.
If the phone is repeatedly very hot, diagnose the cause rather than assuming that a battery replacement alone will fix it.
7. The case or screen is lifting
This is the sign to treat most seriously.
A swollen lithium-ion battery can push against the back cover or display. The phone may rock on a flat surface, develop a gap around the case or have a screen that appears to lift.
Do not squeeze it closed, puncture it or continue charging it to see what happens. Stop charging and arrange professional advice. If the battery is exposed or the device is becoming very hot, minimise handling and keep it away from heat and flammable material.
When should you replace your phone battery?
Replacement becomes a sensible option when battery-related symptoms are persistent, software checks do not explain them and the rest of the phone is still worth keeping.
It is especially worth getting a quote when:
- battery life is the main thing making the phone difficult to use;
- unexpected shutdowns are frequent;
- the phone otherwise works well;
- the repair cost is much lower than replacing the handset.
Read our complete phone battery replacement guide for cost, process and repair-time information.
What can look like a bad battery but is not?
Before booking a replacement for ordinary fast drain, check for:
- a recently installed app running heavily in the background;
- weak mobile reception;
- hotspot use;
- high screen brightness;
- navigation or camera use;
- a major software update still completing background work;
- a damaged charger or cable;
- a dirty or faulty charging port.
If you are not sure whether the battery is the cause, Fonebook's booking flow allows you to choose diagnosis rather than guessing the wrong repair.
Battery age vs battery condition
Two phones bought on the same day can age differently because batteries are affected by charge cycles, temperature and usage patterns.
Apple says batteries in iPhone 14 models and earlier are designed to retain 80% of original capacity at 500 complete cycles under ideal conditions, while iPhone 15 models are designed for 80% at 1,000 cycles under ideal conditions.
That does not mean every battery reaches those figures in exactly the same way, or that 80% is an automatic failure point. Real symptoms matter.
Phone battery replacement at Fonebook
Fonebook Horden shows current supported battery replacement options and prices online. The current phone-battery category starts from £45 for supported models, with exact prices depending on the device.
Check current battery replacement prices or book a diagnosis or repair.
Frequently asked questions
How many years should a phone battery last?
There is no fixed number of years because battery ageing depends on cycles, temperature and use. Look at battery health and real symptoms rather than age alone.
Should I replace my battery at 80% health?
Not automatically. It is a useful reference point. Consider how long the phone lasts, whether it shuts down, whether a service message appears and whether you have applicable warranty or cover.
Can a bad charging port look like a bad battery?
Yes. If the phone charges intermittently, only at an angle or not at all with known-good accessories, the charging system may need diagnosis.
What should I do with a swollen phone?
Stop charging it and seek professional advice. Do not puncture the battery or force the case back together.