What is battery health, and when should you replace the battery?
What battery health means, the signs of a worn battery, when to replace it and the charging habits that help it last longer.
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If your phone no longer lasts as long as it used to, you are looking for a charger before evening, or it suddenly switches off at 20 per cent, the battery is very likely the cause. In this article we explain what battery health means, how to tell when a battery is worn and when it is time to replace it.
What does battery health mean?
The lithium-ion batteries used in phones age chemically as they are used. Battery health is the amount of energy the battery can store today compared with what it could store when new. A battery with 85% health, for example, can hold roughly 85% of its original capacity.
This ageing is normal and happens to every battery. How fast it happens depends on the number of charge cycles, temperature and how the phone is used. One charge cycle means using 100% of the battery's capacity in total, not necessarily in one go. Using 60% one day and 40% the next, for instance, counts as one cycle.
As a battery wears, it doesn't just run down sooner; it also struggles to deliver the bursts of power the phone needs at busy moments. That is why some phones reduce performance slightly to prevent unexpected shutdowns.
Signs of a worn battery
The phone running down much faster than before and needing charging several times a day
The phone switching off suddenly at around 20–30%, especially in cold weather
The percentage behaving erratically, such as dropping from 40% to 15% in one go or jumping up quickly once plugged in
The phone slowing down and apps taking longer to open
Unusual warmth while charging or in normal use
The screen lifting at the edge, a gap appearing in the frame or the back cover bulging: these are signs of a swollen battery and need attention without delay
If you notice one or more of these signs, it is time to check the battery's health.
How to check battery health on an iPhone
On an iPhone, go to Settings > Battery > Battery Health; depending on your iOS version, the name of this section may differ slightly. There you will see the Maximum Capacity figure, which shows how much of its original capacity the battery still has.
According to Apple, a battery whose capacity has dropped below 80% of its original level is considered significantly degraded. In that case you may also see a service recommendation on the Battery Health screen.
Android phones
On Android, this information varies by brand, model and software version. Some models show battery health in the battery settings, while on others it can be checked in the manufacturer's diagnostics or support app. On some phones it isn't shown to the user at all and can only be measured at a repair service.
Battery apps from app stores mostly make estimates, so treat their results as a rough guide rather than an exact measurement. If you are unsure, looking out for the signs above and having the phone checked is the most reliable approach.
When should you replace it?
There is no single cut-off figure; what matters is whether the phone still meets your daily needs. As a general rule, a replacement is worth considering if:
Battery health has fallen below 80%
The phone can't get through the day and this is causing you trouble
Sudden shutdowns or a clear slowdown have started
The battery has swollen: in this case it should be replaced without delay
There is no need to rush if your phone shows 83% health and never lets you down. On the other hand, a phone that shows higher health but keeps switching off may still have a battery problem.
The quality of the replacement battery matters too. On iPhones, if a non-genuine or unverifiable battery is fitted, a message about the part may appear in Settings and battery health information may not be shown.
Swollen battery: stop using the phone
A swollen battery is a damaged battery with gas building up inside it. If it is punctured, crushed or overheated, it can catch fire. If the screen or back cover is bulging, the frame is opening up or the phone rocks on a flat surface, do the following:
Don't charge the phone, and switch it off if you can.
Don't press on the screen or frame to flatten it, and don't try to remove the battery yourself.
Keep the phone on a hard surface, away from heat, sunlight and anything flammable.
Bring it to a repair service as soon as possible.
Habits that help your battery last longer
Keep it away from heat. Heat is a battery's worst enemy. Don't leave the phone in the sun or in a car on a summer day, and don't charge it under a pillow. If it gets very hot while charging, take off a thick case.
Don't leave the battery at 0% for long. Sitting completely flat for a long time wears the battery. If you won't use the phone for a while, store it about half charged.
You don't need to wait for 0% every time. Lithium-ion batteries don't have the “memory” problem of older batteries, so topping up during the day is fine.
Keep optimised charging on. The iPhone's optimised battery charging feature learns your routine and, when needed, holds overnight charging at 80% until shortly before you usually unplug. Many Android phones have similar options that stop charging at a set level or slow down overnight charging; the name varies by brand.
Use a good-quality charger and cable. Poor-quality, uncertified products can damage the battery and the phone.
Avoid heavy gaming while charging. Charging and heavy use at the same time make the phone run very hot.
Getting your battery replaced
A battery replacement is one of the most practical ways to make a tired phone comfortable to use again. At Işıltı İletişim most repairs are done the same day. We give you the exact price after inspecting your device, and we never start work without your approval. If you are in Kahramanmaraş, our free courier collects your phone from your address and returns it after the repair. We never ask for your screen passcode or your iCloud or Google account details.
Choose your model in our price calculator to see pricing information, or visit our battery replacement page for more details.