Replace your iPhone battery when it no longer holds a full day of normal use, when the phone shuts down unexpectedly at 20–30% charge, or when it reaches three to four years old.

iPhones are designed to retain 80% of their original battery capacity after 500 full charge cycles. A charge cycle means draining the battery from 100% to 0% and back to 100% — not necessarily in one day. Most people complete one cycle per day, so a typical iPhone battery lasts three to four years before it noticeably degrades.

You do not have to wait until the battery fails completely. Replacing it before it becomes unreliable is cheaper than repairing water damage or a cracked screen caused by a phone that shuts down unexpectedly in your pocket. A battery replacement costs between $69 and $99 at Apple, depending on your model, and takes one to two hours at most Apple Stores or authorized repair shops.

Key Takeaways

  • Battery health below 80% means the battery is degrading faster than normal and will likely need replacement within the next year.
  • Unexpected shutdowns at 20–30% charge are a sign the battery cannot deliver the power your phone demands, even though it shows charge remaining.
  • iPhones older than three years almost always benefit from a battery replacement, even if the phone still works.
  • You can check your battery's current health in Settings > Battery > Battery Health & Charging on any iPhone running iOS 11.3 or later.

Check your battery health in Settings

Apple built a battery health tool into every iPhone running iOS 11.3 or later. Open Settings, tap Battery, then tap Battery Health & Charging. You will see two numbers: Maximum Capacity (the percentage of the original battery's charge the battery can now hold) and Condition (whether the battery is Normal, Degraded, or Service Recommended).

Maximum Capacity of 80% or higher means your battery is still within normal wear. Below 80%, the battery is degrading faster than expected and you should plan a replacement within the next few months. If Condition shows "Service Recommended" or "Poor Condition," the battery needs replacement now.

This tool is the most reliable way to know whether your battery is the problem. Many people blame a slow phone or poor performance on the battery when the real culprit is storage space, background apps, or an older processor. Checking Battery Health & Charging first saves you from replacing a battery that is not the issue.

Unexpected shutdowns at moderate charge levels

If your iPhone shuts down when the battery shows 20%, 30%, or even 50% charge remaining, the battery is failing. This happens because the battery cannot deliver the power the phone needs at that moment — the processor, screen, and radios all demand current at once, and an aging battery cannot keep up. The phone protects itself by shutting down rather than damaging the battery further.

Restarting the phone usually turns it back on, and the battery percentage will be lower than before. This cycle repeats and gets worse over time. Unexpected shutdowns are inconvenient and risky — your phone could die during a navigation session, a call, or when you need it in an emergency. This is the clearest sign you need a replacement.

Battery age and normal wear patterns

An iPhone battery that is three to four years old has usually completed 1,000 to 1,500 charge cycles. At that point, Maximum Capacity typically sits between 70% and 85%, and you will notice the phone needs charging more often. This is normal wear, not a defect.

If you use your phone heavily — charging it twice a day — the battery will degrade faster. If you charge it once every two days, it will last longer. Keeping the phone cool and avoiding extreme heat also slows degradation. But even with perfect care, a battery older than four years will eventually need replacement.

Replacing the battery at three to four years is often cheaper and easier than waiting for it to fail. A failed battery can cause the phone to shut down without warning, and you may not have time to back up your data or get to a repair shop.

Performance throttling and battery replacement

Starting with iOS 10.2.1, Apple reduced processor speed on iPhones with degraded batteries to prevent unexpected shutdowns. This is called performance throttling. If your phone feels slow and you have not restarted it recently, a degraded battery might be the reason.

You can check whether throttling is active by opening Settings > Battery > Battery Health & Charging. If Maximum Capacity is below 80% and Condition shows Degraded, throttling is likely on. Replacing the battery will restore full processor speed — the phone will feel noticeably faster.

Performance throttling is a safety feature, not a punishment. It keeps the phone running instead of shutting down. But it also means a degraded battery is affecting your daily experience, which is a good reason to replace it.

Where to replace your battery

Apple Stores and authorized Apple repair shops offer battery replacement for $69 to $99, depending on your iPhone model. Older models like the iPhone 8 or earlier cost less; newer models like the iPhone 15 cost more. The replacement usually takes one to two hours, though you can schedule an appointment online to avoid waiting.

Some third-party repair shops charge less — often $40 to $60 — but quality varies widely. If you choose a third-party shop, look for one that uses genuine Apple batteries or high-quality aftermarket batteries, not cheap knockoffs. A bad battery replacement can damage your phone's charging system or cause the battery to fail again within months.

If your iPhone is still under warranty or AppleCare+, battery replacement may be covered at no cost if the battery health has dropped below 80% due to a defect rather than normal wear. Contact Apple Support to check your coverage before paying for a replacement.

When to replace the phone instead of the battery

If your iPhone is five years old or older, or if it has other problems like a cracked screen, water damage, or a failing speaker, replacing the battery alone may not be worth the cost. A battery replacement extends the phone's life by one to two years, but if the phone is already aging, you might be better off upgrading to a newer model.

Compare the cost of a battery replacement to the cost of a new or refurbished iPhone. If the phone is worth less than $300 and the battery costs $80, you are spending 25% of the phone's value on a single repair. If the phone is worth $600 and the battery costs $80, the repair is a better value.

Also consider whether the phone still receives software updates. iPhones older than five to six years may not run the latest iOS version, which means fewer security patches and fewer new features. In that case, upgrading is often the better long-term choice.

Frequently Asked Questions

How many times can I charge my iPhone before the battery wears out?

Apple rates iPhone batteries for 500 full charge cycles while retaining 80% capacity. Most people complete one cycle per day, so this means roughly 500 days or about 18 months of normal use. After 500 cycles, the battery continues to work but degrades faster. By 1,000 cycles (roughly three years), most batteries drop to 70–80% capacity.

Does leaving my iPhone plugged in overnight damage the battery?

No. Modern iPhones stop charging at 100% and hold the charge without drawing current, so leaving the phone plugged in overnight does not degrade the battery faster. However, keeping the battery at 100% for long periods does cause slight degradation over months. If you want to maximize battery lifespan, unplug the phone once it reaches 100% or use Optimized Battery Charging in Settings > Battery > Battery Health & Charging, which limits charging to 80% most of the time.

Can I replace the battery myself?

You can, but it is not recommended unless you have experience with phone repair. Opening an iPhone requires special tools and risks damaging the screen, water seals, or internal components. A mistake can cost more to fix than a professional replacement. Apple and authorized shops handle the replacement safely and back the work with a warranty.

Will replacing the battery fix my slow iPhone?

Only if the slowness is caused by performance throttling due to a degraded battery. Check Battery Health & Charging first. If Maximum Capacity is below 80%, a battery replacement may help. If Maximum Capacity is 80% or higher, the slowness is likely caused by storage space, background apps, or an older processor, and a battery replacement will not fix it.

What is the difference between Maximum Capacity and Condition?

Maximum Capacity shows the percentage of the original battery's charge the battery can now hold — for example, 85% means the battery holds 85% as much charge as it did when new. Condition is Apple's assessment of whether that level of capacity is normal for the phone's age. A three-year-old phone at 75% capacity might show Condition as Degraded, while a one-year-old phone at 75% would show Normal.