Maximum Capacity Tells You How Much Charge Your Battery Can Hold Now
Maximum capacity is the percentage of charge your iPhone battery can hold compared to when it was brand new. If your battery shows 80% maximum capacity, it means the battery can now hold only 80% of the charge it held on the day you bought the phone. This number drops over time because all rechargeable lithium batteries naturally lose their ability to store energy with repeated charging cycles.
You find this number in Settings > Battery > Battery Health & Charging on any iPhone running iOS 16 or later. On older versions, it appears under Settings > Battery > Battery Health. The percentage shown is Apple's measurement of your specific battery's current condition, not a prediction of how long it will last before you need to replace it.
Key Takeaways
- Maximum capacity shows what percentage of the original charge your battery can now hold, and it naturally decreases over time as you charge and use your phone.
- A battery at 80% maximum capacity still works normally for most people, but you may notice your phone drains faster than it did when new.
- Reaching 80% maximum capacity does not automatically trigger any changes to your phone's performance, though Apple may eventually slow the processor if the battery becomes very degraded.
- You can slow the rate of capacity loss by keeping your phone between 20% and 80% charged, avoiding extreme temperatures, and enabling Optimized Battery Charging in settings.
Why Maximum Capacity Drops Over Time
Lithium batteries degrade because of the chemical reactions that happen inside them every time you charge and discharge. Each cycle causes tiny damage to the battery's internal structure. After hundreds of charge cycles, the battery cannot hold as much energy as it once did. This is not a defect—it is how lithium chemistry works, and it happens in every rechargeable battery in phones, laptops, and electric cars.
The rate of capacity loss depends on how you use your phone. Charging to 100% frequently, leaving your phone plugged in overnight, exposing it to heat, and draining it completely all speed up degradation. A battery that starts at 100% maximum capacity might drop to 90% after 500 charge cycles, or it might take 800 cycles—it varies based on your charging habits and the temperature where you keep your phone.
What Maximum Capacity Means for Your Phone's Speed
Apple slows down your iPhone's processor when the battery becomes very degraded, but this does not happen at 80% maximum capacity. The slowdown only kicks in if your battery reaches around 20% maximum capacity or lower, or if the battery cannot deliver the power the processor needs in a single moment. This feature, called performance management, prevents your phone from shutting down unexpectedly when the battery is too weak to handle peak power demands.
If your battery is at 80% maximum capacity, your phone runs at full speed. You will not see any performance slowdown. What you may notice is that your phone drains faster than it used to—a battery at 80% capacity straightforward cannot store as much energy, so you might need to charge it more often during the day. This is different from slowdown; it is just the reality of a battery that has aged.
How to Check Your Battery's Maximum Capacity
Open Settings on your iPhone and tap Battery. Then tap Battery Health & Charging. You will see two numbers: Maximum Capacity (shown as a percentage) and Cycle Count (the number of complete charge cycles your battery has gone through). The maximum capacity percentage is what tells you the current state of your battery's health.
If you have an older iPhone running iOS 15 or earlier, the path is Settings > Battery > Battery Health. The display looks slightly different, but the maximum capacity number means the same thing. You can also see battery health information in the Apple Support app or by taking your phone to an Apple Store, where they can run a more detailed diagnostic.
Ways to Slow Down Capacity Loss
You cannot stop your battery from degrading, but you can slow it down. Keep your iPhone between 20% and 80% charged as much as possible—avoid letting it drain all the way to 0% or charging it to 100% every single day. Store your phone in a cool place; heat is one of the biggest enemies of battery health. If you live somewhere hot or use your phone while charging, the battery will degrade faster.
Enable Optimized Battery Charging in Settings > Battery > Battery Health & Charging. This feature learns when you usually charge your phone and slows down charging to 80% until you need the full charge, which reduces the time your battery spends at 100%. You can also turn on Low Power Mode when your battery drops below 20%, which reduces background activity and slows down drain.
Avoid using your phone while it is charging, especially with a case on, because this generates heat. Do not leave your phone plugged in overnight if you can help it. If you know you will not use your phone for weeks, charge it to about 50% and store it in a cool place rather than leaving it fully charged or fully drained.
When to Consider a Battery Replacement
Apple recommends replacing your battery when maximum capacity drops below 80%, though many people find their phone still works fine at that level. If your battery is at 80% and you are happy with how long your phone lasts on a single charge, there is no urgent reason to replace it. If you are at 50% maximum capacity and your phone drains in a few hours, a replacement will make a noticeable difference.
You can have your battery replaced at an Apple Store, an Apple Authorized Service Provider, or through Apple's mail-in repair service. The cost varies by iPhone model but typically ranges from $50 to $70. If your phone is still under warranty or covered by AppleCare+, the replacement may be free. Some third-party repair shops also replace iPhone batteries, often for less money, though Apple's parts and warranty are generally considered more reliable.
Frequently Asked Questions
Does 80% maximum capacity mean my battery will die soon?
No. A battery at 80% maximum capacity still holds a useful amount of charge and can last for years. It straightforward cannot hold as much energy as it did when new, so you may need to charge it more often. Most people do not notice a significant problem until capacity drops below 70%.
Can I improve my battery's maximum capacity once it has dropped?
No. Maximum capacity only goes down, never up. Once your battery has degraded to 80%, it will not return to 100%. You can only slow the rate at which it continues to drop by following good charging habits and keeping your phone cool.
Why does Apple slow down my phone if the battery is bad?
A degraded battery cannot deliver power as quickly as a new one. When your processor tries to draw more power than the battery can supply, your phone shuts down to protect the battery. Slowing the processor prevents these unexpected shutdowns by reducing power demand. You can turn off this feature in settings, but your phone may shut down during heavy use.
Is it normal for maximum capacity to drop 10% in the first year?
It varies. If you charge your phone to 100% every day and use it heavily, dropping to 90% in a year is normal. If you use Optimized Battery Charging and keep your phone cool, you might still be at 95% or higher. The first 10% of capacity loss usually happens faster than the rest.
Should I replace my battery at 80% or wait until it gets lower?
That depends on your needs. If you use your phone all day and do not want to charge it during the day, replace it sooner. If you are near a charger most of the time, you can wait until capacity drops further. There is no magic number—replace it when the battery life no longer meets your needs.