How to Check iPhone Battery Health (and When to Replace the Battery)

Your iPhone keeps a running score of how worn its battery is, and it is worth checking a few times a year. That number tells you whether a phone that feels slow or dies early needs a new battery, a settings tweak, or nothing at all.

This guide explains how to check iPhone battery health, what the percentage really means, why your phone may say "Service" or "Unknown Part," and the point at which replacing the battery is clearly the right move.

How to Check iPhone Battery Health

On any iPhone running a recent version of iOS:

1. Open Settings.
2. Tap Battery.
3. Tap Battery Health (on some versions it is labeled Battery Health & Charging).

You will see Maximum Capacity as a percentage. On iPhone 15 and newer you will also see Cycle Count, the manufacture date, and the first-use date on this same screen or under Settings, General, About.

On older iPhones the cycle count is not displayed in Settings. A repair shop can read it with diagnostic tools, and we include that readout in our free battery health check.

What Maximum Capacity Actually Means

Maximum Capacity compares how much charge your battery can hold today against how much it held when it was new. A reading of 85% means a full charge now delivers 85% of the runtime it did on day one.

Every lithium-ion battery loses capacity with use. The rate depends on cycles, heat, and charging habits, but a typical iPhone battery lands somewhere around 80% after two to three years of normal use.

The 80% Line

Apple treats 80% as the threshold where a battery is "worn." Under warranty or AppleCare, Apple will replace a battery that drops below 80% within the coverage period. Outside of coverage, 80% is still the right rule of thumb for when replacement starts to pay off.

Below 80% the drop-off is not linear in how it feels. A phone at 79% is often noticeably worse to live with than one at 85%, because the battery's ability to deliver bursts of power falls along with its capacity.

Cycle Count

One cycle equals using 100% of the battery's capacity, not one charge. Using 50% today and 50% tomorrow is one cycle. Apple rates recent iPhone batteries to retain 80% capacity at around 1,000 cycles, and older models at around 500. If you are near or past that count, replacement is due regardless of the percentage shown.

Peak Performance Capability and Throttling

Under Maximum Capacity there is a section called Peak Performance Capability. This is where iOS tells you whether it is slowing the phone down to protect it.

• "Your battery is currently supporting normal peak performance" means no throttling is active.
• A message about an unexpected shutdown and performance management means the battery could not deliver enough power at some point, the phone shut off, and iOS is now limiting speed to prevent it happening again. This is the classic "my iPhone feels slow" cause.
• "Your battery's health is significantly degraded" with a Service note is iOS telling you directly that the battery should be replaced.

If performance management is on, a new battery removes it. The phone goes back to full speed immediately, which is why a battery replacement often feels like getting a new phone.

What "Unknown Part" or "Service" Means

If your battery was replaced previously and the screen shows Unknown Part, the phone could not verify the battery as a genuine Apple part. It does not necessarily mean the battery is bad. It means it is aftermarket, or it is a genuine battery that was not paired to the phone through Apple's process. On some models, Maximum Capacity will not be displayed at all for a non-verified battery.

We offer both genuine Apple batteries and premium aftermarket batteries and explain the difference before you choose. Our earlier post on iPhone battery replacement cost goes into the trade-offs.

Signs the Number Is Not Telling the Whole Story

Battery Health is an estimate, and it can lag behind reality. Watch for these symptoms even if the percentage looks fine:

• The phone jumps from 30% to 5% or shuts off with charge remaining.
• It dies quickly in cold weather.
• It gets warm while idle or charges unusually slowly.
• The screen is lifting on one edge. That is a swelling battery and needs attention right away.
• The percentage reads much higher than the runtime you are getting.

A professional battery test measures the actual capacity under load, which catches batteries that Settings still rates as healthy. That test is part of our free diagnostic, so you do not have to guess.

How to Slow Down Battery Wear

• Turn on Optimized Battery Charging in the Battery Health screen so the phone waits to finish charging until you usually unplug.
• Use a charge limit if your iPhone offers one. Stopping at 80% or 90% for daily use meaningfully extends battery life.
• Avoid heat. Heat ages a battery faster than anything else. Do not leave the phone on a dashboard or charge it under a pillow. Our post on iPhone overheating has more.
• Use certified chargers. Cheap adapters deliver unstable power that stresses the battery.
• Do not obsess over it. The battery is a consumable. Replacing it every few years is normal and inexpensive compared to a new phone.

When to Replace an iPhone Battery

Replace it if any of the following are true:

• Maximum Capacity is at or below 80%.
• iOS shows a Service message or has enabled performance management.
• The phone shuts off unexpectedly or cannot get through a normal day.
• The battery is swollen.

At our Glendale shop, a battery replacement takes about 30 minutes. Current pricing as of this writing runs from $49 on the iPhone 11 to $119 for a genuine Apple battery on the iPhone 16 and 17 series, with premium aftermarket options from $59 to $99 on most models. Live pricing for your exact model is in our booking system.

Get a Free Battery Health Check in Glendale

Not sure what your number means for your phone? Bring it by Pro iPhone Repair. We will run a full battery diagnostic at no charge, give you a printed report with true capacity and cycle count, and tell you honestly whether a replacement is worth it. Book a free battery check or walk in any time we are open.