A battery is the only part of an iPhone that wears out by design. Knowing how to read its health tells you whether your phone needs a new battery, a new owner, or nothing at all, and it is the first thing to check before buying a used one.
What the percentage means
Open Settings, Battery (on older models, Settings, Battery, Battery Health & Charging). The Maximum Capacity figure compares your battery's capacity today with when it was new. At 90%, a full charge holds 90% of the energy it did on day one.
Below it, Peak Performance Capability tells you whether the battery can still deliver the power the processor asks for. When it cannot, iOS may slow the phone down to avoid unexpected shutdowns, and it says so on that screen.
What Apple promises
Apple counts wear in charge cycles: one cycle is using 100% of the battery's capacity, whether in one go or spread over several days. According to Apple's support pages:
| Model | Designed to keep 80% of original capacity after |
|---|---|
| iPhone 14 and earlier | 500 complete charge cycles |
| iPhone 15 and later | 1,000 complete charge cycles |
Those are design targets "under ideal conditions", not guarantees. Heat is the main enemy: a phone that charges in a hot car or gets warm while gaming will lose capacity faster.
When to replace the battery
80% is the practical line. It is where Apple's design target ends, and AppleCare covers a free battery replacement when capacity falls below 80%. iOS also shows a service message when the battery has significantly degraded.
In daily terms:
- Above 90%: nothing to do.
- 85 to 90%: normal for a phone two or three years old. You lose an hour or two of a day's use.
- 80 to 85%: plan a replacement within the year, especially if the phone no longer lasts until evening.
- Below 80%, or a service message: replace the battery if you want to keep the phone, or factor it into the price if you sell it.
A new battery is almost always cheaper than a new phone. Apple and independent repairers quote the price per model; Apple shows its estimate on its battery service page before you book.
How to slow the decline
- Use the 80% limit (iPhone 15 and later). In Settings, Battery, Charging, you can cap charging at 80, 85, 90, 95 or 100%. Apple recommends 95% as a balance; 80% helps most if you rarely need a full battery. The phone still charges to 100% occasionally to keep its estimates accurate.
- Leave Optimized Battery Charging on (iPhone 14 and earlier, and at 100% on newer models). It learns your routine and waits at 80% until shortly before you usually unplug.
- Avoid heat. Do not charge under a pillow, in direct sun or in a hot car. Take the phone out of a thick case if it gets warm while charging.
- Do not chase 0%. Lithium-ion batteries do not need full discharges.
Buying a used iPhone? Check this first
Ask the seller for a screenshot of Maximum Capacity, or check it yourself. Then look at Settings, General, About, Parts and Service History: it shows if the battery was replaced and whether the part is genuine. A used iPhone 15 or later at 85% has far more life left than an iPhone 14 at 85%, because its battery is rated for twice as many cycles. More in new vs refurbished.
Quick answers
Is 80% battery health bad on an iPhone?
It is the point where Apple considers the battery worn: AppleCare replaces it below 80%. The phone still works, but expect noticeably shorter days.
How many charge cycles does an iPhone battery last?
Apple designs the iPhone 15 and later to keep 80% of their capacity after 1,000 complete charge cycles, and the iPhone 14 and earlier after 500.
Should I limit charging to 80%?
On an iPhone 15 or later, if you rarely need a full battery, yes: it reduces wear. Apple suggests 95% as a balance between battery life today and battery health later.
