Every lithium-ion battery wears down with use, and your iPhone keeps a running estimate of how much life is left in its own. That estimate is tucked inside Settings, and checking it takes less than a minute. Knowing the number helps you decide whether a short battery life is down to your habits, a software issue, or a genuinely tired battery that needs replacing.
What battery health actually measures
The headline figure is called Maximum Capacity. It is shown as a percentage and compares your battery’s current capacity against the day it left the factory. A reading of 100 percent means the battery still holds a full charge. A reading of 85 percent means a full charge now holds roughly as much energy as a brand-new battery charged to 85 percent, so you get noticeably less screen time between charges.
Apple designs iPhone batteries to retain up to 80 percent of their original capacity after 500 complete charge cycles under normal conditions. For most people that takes around two years of daily use, though heavy chargers reach it sooner. Dropping below 80 percent is not a fault; it is expected ageing, and it is the point at which many people start thinking about a replacement.
Check battery health on iPhone
- Open the Settings app on your iPhone.
- Scroll down and tap Battery.
- Tap Battery Health. On iPhone 15 models and later this entry is labelled Battery Health & Charging, and on some newer versions of iOS the capacity reading sits under a Charging section.
- Read the number next to Maximum Capacity. This is your battery’s current health.
While you are on that screen, look at the Peak Performance Capability line underneath. On a healthy battery it reads that the battery is supporting normal peak performance. If the battery has aged badly or shut down unexpectedly, iOS may apply performance management to prevent further sudden shutdowns, and this line will say so. You can usually turn that management off from the same screen if you prefer full speed and accept the risk of the occasional shutdown.
Reading the warning messages
If Maximum Capacity falls far enough, or the battery can no longer deliver the power the phone needs, you may see a message such as Service or a note that your battery’s health is significantly degraded. That is iOS telling you a replacement would restore full capacity and performance. The phone keeps working, but you will feel the shorter runtime.
See how much power apps are using
The main Battery screen does more than show health. Scroll down and you will find charts of battery level and activity over the last 24 hours or the last 10 days, plus a breakdown of Battery Usage By App. If one app is draining a surprising share of your battery, this is where you will spot it. A worn battery and a greedy app can feel identical from the outside, so checking both together gives you the full picture.
If your iPhone doesn’t show Battery Health
The Battery Health screen arrived with iOS 11.3. If your iPhone is too old to run that version, the option simply will not appear, and there is no built-in way to read the capacity percentage. In that case you can book a visit with Apple or an authorised service provider, who can run a diagnostic on the battery and give you a condition reading. Third-party apps that claim to show precise battery health on older devices are estimating from indirect data and are not as reliable as Apple’s own figure.
Habits that slow battery ageing
You cannot stop a battery ageing, but you can slow it. Heat is the biggest enemy, so avoid leaving the phone in a hot car or in direct sun while charging. iOS also includes Optimized Battery Charging, which learns your routine and holds the charge at 80 percent until just before you normally unplug, reducing the time the battery spends full. Newer iPhones add an 80 percent charge limit you can set manually. Both features live in the same Battery settings area and are worth leaving on.
How often should you check?
There is no need to watch the number daily; the capacity moves slowly. Checking every couple of months, or whenever battery life suddenly feels worse, is plenty. A single low reading after a cold day or a heavy session is normal, so look for a lasting trend rather than reacting to one figure. If Maximum Capacity has settled well below 80 percent and you are reaching for the charger before lunch, that is the clearest sign it is time for a new battery.
Why the number can jump around
Do not be alarmed if Maximum Capacity seems to wobble by a point or two, or if it appears to drop a few percent and then recover. The figure is an estimate the iPhone recalculates as it learns the battery’s behaviour over many charge cycles, and extreme cold or heat can temporarily skew a battery’s apparent capacity. After a major iOS update the reading can also shift slightly as the system recalibrates. What matters is the direction of travel over months, not a single snapshot. If you want the most accurate picture, read the number when the phone is at room temperature and not in the middle of a heavy charging or gaming session.
What a battery replacement restores
If your reading points to a worn battery, a replacement is usually far cheaper than a new phone and brings back both the runtime and any lost peak performance. After a genuine Apple or authorised replacement, Maximum Capacity resets to 100 percent and the performance management message, if you had one, disappears. Be aware that fitting a non-genuine battery can cause iOS to show a warning that it cannot verify the part, and on some models the Battery Health readout may become unavailable with an unofficial cell. For that reason, having the battery replaced through Apple or an authorised provider keeps the health reporting working as designed.
A quick recap
Battery health lives in Settings > Battery > Battery Health, and the Maximum Capacity percentage is the figure that matters. Above 80 percent is considered healthy; below it, you are on borrowed time and a replacement will bring back the runtime you remember. Pair that number with the per-app usage charts on the same screen and you will almost always find the real reason your iPhone is not lasting the day.
