iPhone Battery Health Explained: What Percentage Is Good?

Open Settings on an iPhone, go to Battery, then Battery Health, and you will see a percentage called Maximum Capacity. It is one of the most useful numbers when buying a used iPhone, and also one of the most misunderstood.

What the number means

Maximum Capacity compares your battery with what it could hold when it was new. At 85%, the battery can hold about 85% of its original charge. A brand-new phone starts at or near 100%.

All lithium-ion batteries wear down as they are charged and discharged. Heat speeds this up. Apple says that iPhone batteries are designed to retain up to 80% of original capacity after 500 complete charge cycles for most models, and iPhone 15 models and later are rated for 1,000 cycles under ideal conditions.

What is a good figure on a used iPhone?

As a rough guide:

• 90% and above: very good for a used phone.
• 85–89%: acceptable and common on phones a few years old.
• 80–84%: usable, but you will notice shorter battery life.
• Below 80%: plan for a replacement. iOS may also display a service message.

A phone with a low number is not necessarily a bad buy. It simply needs a lower price to allow for a replacement battery.

Beware of "100%" on an old phone

An old phone showing exactly 100% may have had its battery replaced, which is fine if the work was done well. But the number on its own does not tell you the quality of that replacement. On newer iPhones, a replaced battery may trigger a message in Settings if it is not recognised as a genuine Apple part. Look in Settings, General, About for any parts notices. Our Ex-UK checklist includes this.

Peak Performance Capability

Below the percentage, iOS tells you whether the battery can deliver peak performance. If the phone has shut down unexpectedly because of a weak battery, iOS may slow it slightly to prevent another shutdown. If you see that message on a phone you are buying, treat it as a sign the battery needs replacing.

How to keep a battery healthy

• Avoid heat. Do not leave the phone on a car dashboard, a common cause of damage in Kenya's sun.
• Leave Optimised Battery Charging switched on.
• Avoid regularly charging in hot conditions, such as under a pillow.
• Use a reputable charger. Very cheap chargers can give unstable power.
• Do not worry about occasional full charges. Normal charging habits are fine.

Fast charging is not something to fear. Keep the phone cool and it does its job safely.

When to replace the battery

Replace it when the phone no longer lasts your normal day or when health drops well below 80%. A fresh battery can make an older iPhone feel renewed at a fraction of the price of a new phone. See our guide to phone repairs. Until you do, a power bank can keep you going.

Compare with total cost

When comparing two used iPhones, add the expected cost of a new battery to the cheaper one if its health is low. A slightly more expensive phone with a healthy battery may turn out to be cheaper overall.