Check your battery health in Settings

Your iPhone tracks how much capacity your battery has lost over time and stores that information where you can see it. Open Settings, then tap Battery, then Battery Health & Charging. You will see a percentage labeled Maximum Capacity — this is what matters. A new iPhone shows 100%. As you use it, this number drops.

The second number you see is Cycle Count (on iPhone 11 and newer). This counts how many times you have fully charged and fully drained the battery. Neither number is a pass-or-fail test. They are just measurements of wear.

Key Takeaways

  • Maximum Capacity shows what percentage of the battery's original power remains; 80% or higher is normal for an older phone, while anything below 50% means the battery is significantly degraded.
  • Cycle Count tells you how many full charge-drain cycles the battery has been through, and higher numbers do not automatically mean the battery is failing.
  • Your iPhone may slow down performance when the battery is very degraded to prevent sudden shutdowns, a feature called performance management.
  • If Maximum Capacity drops below 50% or your phone shuts down unexpectedly, you can have Apple replace the battery at an Apple Store or authorized repair shop.

What the Maximum Capacity percentage actually means

Maximum Capacity is a percentage of the battery's original charge. If it shows 85%, your battery can now hold 85% of the power it held when new. This is normal degradation — lithium batteries lose capacity every time they charge, and there is no way to stop it.

A phone that is one or two years old and shows 85% to 95% is working as designed. A phone that is three to four years old and shows 75% to 85% is also normal. The battery does not suddenly fail at any particular number. Instead, you will notice the phone needs charging more often as the percentage drops.

If Maximum Capacity falls below 50%, the battery has degraded significantly. At this point, you may notice the phone dies faster than it should, or shuts down unexpectedly even when the battery percentage shows 20% or 30% remaining.

Performance management and unexpected shutdowns

When a battery is very degraded, it cannot deliver power as quickly as the phone's processor demands. To prevent the phone from shutting down suddenly, Apple built in performance management — the phone automatically reduces its speed when the battery is weak. You will not see a warning; the phone just becomes slower.

If you see a message in Settings that says "Peak Performance Temporarily Reduced" or "Performance Management Enabled," your battery is the reason. This is not a malfunction. It is the phone protecting itself.

You can turn off performance management in Settings > Battery > Battery Health & Charging, but doing so means the phone may shut down without warning when the battery cannot keep up with demand. Most people leave it on.

When to replace your battery

You do not have to replace the battery at any particular capacity number. Replace it when the phone's behavior bothers you — when it dies too fast, when it shuts down unexpectedly, or when you plan to keep the phone for another year or two and want it to feel new again.

If Maximum Capacity is above 80% and the phone is working fine, there is no reason to replace it. If it is below 50% or the phone is shutting down unexpectedly, replacement makes sense.

Apple replaces batteries at Apple Stores and at authorized repair shops. The cost varies by iPhone model but typically ranges from $50 to $80. Some carriers and retailers also offer battery replacement, though Apple's service is usually the most straightforward.

Factors that affect battery health

Battery capacity drops faster if you regularly charge to 100% and let it drain to 0%, if you use the phone in very hot conditions, or if you use demanding apps constantly. None of these will destroy your battery overnight, but they do speed up normal wear.

Charging to 80% and keeping the phone between 20% and 80% charge extends battery life, but most people do not do this and their phones work fine. If you want to slow degradation, enable Optimized Battery Charging in Settings > Battery > Battery Health & Charging. This learns your charging habits and holds the battery at 80% until you need it to charge higher, which reduces wear over time.

Temperature matters more than charging habits. Avoid leaving your iPhone in hot cars or direct sunlight for long periods. Cold does not damage the battery permanently, but it does make it perform worse temporarily.

Reading Cycle Count

Cycle Count (visible on iPhone 11 and newer) tells you how many times the battery has gone through a full charge-and-drain cycle. Apple rates iPhone batteries for around 500 cycles before capacity drops to 80%. A phone that is two years old might have 200 to 400 cycles, depending on how often you charge it.

Cycle Count is informational, not a warning sign. A phone with 400 cycles and 90% capacity is aging normally. A phone with 200 cycles and 60% capacity suggests the battery was damaged or the phone was used in poor conditions. Neither number tells you whether to replace the battery — Maximum Capacity does.

Frequently Asked Questions

Why does my Maximum Capacity say 100% but my phone still dies fast?

Maximum Capacity measures the battery's chemical capacity, not how long the phone lasts on a charge. A phone with 100% capacity can still die fast if you are using demanding apps, if background refresh is on, or if your screen brightness is high. Check Settings > Battery > Battery Usage to see which apps are draining power.

Can I improve my battery health once it drops?

No. Battery capacity only goes down as the battery ages. You cannot restore it by changing settings, updating software, or using special apps. The only way to get a phone back to 100% capacity is to replace the battery.

Is it bad to leave my iPhone plugged in overnight?

Modern iPhones charge to 100% and then stop, so leaving it plugged in does not overcharge it. However, keeping the battery at 100% constantly does speed up degradation slightly. If you want to minimize wear, unplug it once it reaches 100%, or enable Optimized Battery Charging.

What does "Peak Performance Temporarily Reduced" mean?

It means your battery is too degraded to handle the phone's full speed, so the phone is running slower to prevent shutdowns. This is temporary — it happens when the battery is weak, and the phone returns to normal speed once the battery charges higher.

Should I replace the battery or buy a new phone?

If the phone is otherwise working well and you want to keep it, battery replacement is much cheaper than a new phone. If the phone is old, slow, or has other hardware problems, a new phone might make more sense. Battery replacement alone costs $50 to $80 and usually takes a few days.