iPhone Battery Health Explained: What the Percentage Means and What’s Good on a Pre-Owned iPhone

When you shop for a pre-owned iPhone, one number tells you more about day-to-day life with the phone than almost anything else: its battery health. A screen or a camera either works or it doesn’t, but a battery ages a little every time it’s used, so two phones of the same model can last very differently through a day.

Where to find your iPhone’s battery health

Open Settings, tap Battery, then Battery Health (called Battery Health & Charging on some models and iOS versions). You’ll see two things:

• Maximum Capacity: the percentage most people mean when they talk about battery health.
• Peak Performance Capability: whether the battery can still deliver the power the phone asks for at busy moments.

What “Maximum Capacity” really means

Every lithium-ion battery slowly loses some of the charge it can hold as it ages. Maximum Capacity measures that loss against the battery when it was new. A phone at 90% holds roughly 90% of the charge it did on its first day, so a full charge lasts a little less long.

It doesn’t mean the battery is 10% “broken”. Nothing fails at a particular percentage. The phone simply runs for a bit less time between charges as the number goes down.

Why battery health drops: charge cycles

Apple measures battery use in charge cycles. A cycle is using 100% of the battery’s capacity in total, not necessarily in one go: using 60% one day and 40% the next counts as one cycle.

According to Apple, batteries in iPhone 14 models and earlier are designed to keep 80% of their original capacity at 500 complete charge cycles, and batteries in iPhone 15 models and later at 1,000 complete charge cycles, under ideal conditions. Real-world results depend on how the phone is used and charged, and above all on temperature.

Peak performance and the “Service” message

As a battery wears, it can find it harder to deliver sudden bursts of power. If an iPhone shuts down unexpectedly because the battery couldn’t keep up, iOS may manage performance to stop it happening again, and the Battery Health screen will say so.

If the battery is significantly degraded, the same screen shows a Service recommendation. That’s your cue to have the battery replaced, which brings the phone back to full capacity.

What’s a good battery health on a pre-owned iPhone?

There’s no official scale, but this is a practical way to read the number when you shop:

• 95–100%As good as new. Battery life very close to the original.
• 90–94%Excellent. Most people won’t notice a difference from new in a normal day.
• 85–89%Very good. A full day of normal use is comfortable; heavy users may top up in the evening.
• 80–84%Fine for everyday use, with a little less headroom on long days.
• Below 80%Apple considers the battery due for service. Budget for a replacement, or choose a higher figure.

Two phones with the same percentage can still behave differently. A newer model with a more efficient chip and a bigger battery will usually outlast an older one at the same health, so weigh the model and the percentage together.

How to keep your battery health high for longer

1. Keep it cool. Apple’s comfort zone for iPhone is 16 °C to 22 °C, and it advises against exposing it to temperatures above 35 °C. In a South African summer, that means no charging on a sunny dashboard or windowsill.
2. Leave Optimised Battery Charging on. It learns your routine and waits to finish charging past 80% until you need the phone. You’ll find it in Settings > Battery, under Battery Health & Charging or Charging, depending on your model.
3. Consider the 80% limit on iPhone 15 and later. These models let you cap charging at 80% in the same charging settings. If you rarely run low, it reduces wear.
4. Take off a thick case if it gets hot while charging. Apple notes that some cases can trap heat during charging.
5. Keep iOS up to date. Updates include improvements to battery management.
6. Use a good-quality cable and charger. Certified accessories charge safely and as designed.

How we handle battery health at Prime Phones

Every phone we sell is a single, specific device, so we tell you its exact battery health before you buy:

• Measured on that phone. Battery health is part of the 80+ point M360 diagnostic test every device goes through before it’s listed, and the figure is published on the phone’s own product page.
• Tested against what we say. Where a listing states a minimum battery health, the device is checked against that figure before dispatch.
• Covered for 3 months. The battery has its own 3-month warranty, alongside the 6-month warranty on the device. Normal battery wear over time isn’t a fault.

Our condition guide explains how we grade the rest of the device.

Battery health FAQs