How to check battery health on an Android phone
A battery slowly loses capacity as it is charged and discharged. On a used phone it is one of the most expensive surprises, so check it before you pay.
Where to look on the phone
- Settings, Battery: some newer phones show a battery health or maximum capacity figure here.
- Samsung: the Samsung Members app, Support, Phone diagnostics, Battery status.
- Others: many phones show nothing about health. Then an app has to measure it.
What the numbers mean
- 90 to 100 percent: like new.
- 80 to 90 percent: normal for a phone used one or two years.
- Below 80 percent: noticeably shorter days; count a battery replacement into the price.
Quick checks by hand
- Play a video at full brightness for five minutes and watch the percentage. A drop of several percent is a warning.
- Touch the back while the phone is idle: it should not be warm.
- Look along the edges: a lifting screen or back means a swollen battery. Do not buy it.
Knowfone reads the battery's reported capacity against the design capacity, watches the voltage under a short load, checks the temperature and tells you plainly whether the battery is fine or worn, as part of a 7-minute check of the whole phone.
Questions
What battery health is too low?
Below about 80 percent of the original capacity, most people notice the phone needs charging much more often. Below 70 percent a replacement is usually worth it.
Where does Android show battery health?
It depends on the maker and the Android version. Some newer phones show it in Settings under Battery. On Samsung phones the Samsung Members app has a battery check under Phone diagnostics. Many other phones show nothing, so an app is needed.
Can an app measure battery health in one go?
An app can read the charge counter and design capacity that many phones report, watch how the voltage drops under load and check the temperature. Apps that learn the real capacity from your charging over days are more exact, but a used-phone check needs an answer in minutes.
What are signs of a bad battery?
The phone turns off above zero percent, the percentage jumps down quickly under load, the phone gets hot when idle, or the screen or back is lifting. A swollen battery is a reason not to buy.