Replace your iPhone battery when it drops below 80 percent health, or sooner if you notice the phone shutting down unexpectedly during normal use

Apple's battery health feature, built into every iPhone running iOS 11.3 or later, shows you the percentage of your battery's original capacity that remains. You find it in Settings > Battery > Battery Health & Charging. At 80 percent health, your battery has lost about one-fifth of its ability to hold a charge — enough that most people notice shorter time between charges. Below 80 percent, the decline accelerates, and Apple's own documentation recommends replacement at this threshold.

The practical reason to replace at 80 percent is that you'll start experiencing real inconvenience before you reach it. A battery at 75 percent health might last only six or seven hours of mixed use instead of the original ten or twelve. At 60 percent, your phone may shut itself down at 20 or 30 percent battery remaining, even though the display shows higher. This is Apple's safety feature preventing damage to the phone's logic board — but it makes the phone unreliable to carry.

Key Takeaways

  • Check your battery health in Settings > Battery > Battery Health & Charging; this percentage shows how much of the original capacity remains.
  • Apple recommends replacement when health drops to 80 percent or below, though you may notice inconvenience before reaching that point.
  • Unexpected shutdowns at 20–30 percent battery are a sign the battery needs replacement, regardless of the health percentage shown.
  • Battery health degrades fastest in the first two years; after that, degradation typically slows unless you expose the phone to heat or use fast-charging constantly.
  • You can replace the battery through Apple, an Apple Authorized Service Provider, or an independent repair shop, each with different costs and warranty terms.

How battery health percentage actually works

Your iPhone's battery is a lithium-ion cell that loses capacity every time it charges and discharges. The health percentage measures the maximum charge the battery can now hold compared to when it was new. A battery at 90 percent health can hold 90 percent of its original charge; at 70 percent, it holds 70 percent. This is not the same as your current charge level — that's the separate percentage you see in the status bar.

The phone calculates health by measuring how much current the battery can deliver and how much charge it can store, then comparing those numbers to the original specifications. You cannot manually reset this number or "recalibrate" it back up. Once capacity is lost, only replacing the battery restores it.

Health degrades fastest in the first year or two of ownership, then more slowly afterward — unless you regularly expose the phone to heat above 95 degrees Fahrenheit, use fast-charging every day, or let the battery drain completely and sit uncharged for weeks. Normal use in a normal climate typically brings a battery to 80 percent health somewhere between 18 and 36 months.

Signs your battery needs replacement before it reaches 80 percent

Sometimes the health percentage alone doesn't tell the full story. If your phone shuts down unexpectedly when the battery shows 20, 30, or even 40 percent remaining, the battery needs replacement regardless of what the health number says. This shutdown happens because the battery can no longer deliver the current the phone's processor demands, even though charge remains chemically stored in the cell.

Other signs include the phone running noticeably slower under load (opening apps, taking photos, or using GPS), the screen dimming suddenly during normal use, or the phone refusing to charge past a certain percentage. These are all battery-related issues that replacement will fix.

If you see a message in Settings saying "Your battery's health is significantly degraded" or "Service Recommended," Apple is flagging the battery as defective and replacement is the intended next step. This message appears when health drops below a certain threshold or when the phone detects a fault in the cell itself.

Where to replace your iPhone battery

You have three main routes: Apple directly, an Apple Authorized Service Provider, or an independent repair shop. Each has trade-offs in cost, speed, and warranty.

Apple Stores and Apple Mail-In Service cost between $69 and $99 depending on your iPhone model, and the replacement comes with a one-year limited warranty covering the new battery. If your phone is under AppleCare+, battery replacement is usually $0 if the health has genuinely degraded. You can book an appointment online or mail the phone in; in-store service typically takes one to three hours, while mail-in takes five to seven business days plus shipping time.

Apple Authorized Service Providers (you can find them at apple.com/support) charge the same as Apple and offer the same warranty, but may have different availability and wait times depending on your location. Some are local repair shops that Apple has certified; others are big-box retailers with Genius Bar equivalents.

Independent repair shops typically charge $40 to $60 and can often do the work same-day or next-day. The warranty on the battery itself is usually one year, but you lose any remaining manufacturer coverage on the phone if the shop is not Apple-certified. The trade-off is lower cost and faster turnaround, but less recourse if something goes wrong.

What happens to your phone during battery replacement

The technician removes the screen, disconnects the battery connector, and unglues the old battery from the case. They then glue in a new battery, reconnect it, and reseal the screen. The whole process takes 30 minutes to an hour. Your data stays on the phone — the battery replacement does not erase anything.

After replacement, your health percentage resets to 100 percent. The phone will then degrade at the normal rate. You should see noticeably longer battery life when ready; if you don't, the issue may not have been the battery, and you should contact the service provider.

Can you extend battery life without replacing it

You cannot restore lost capacity, but you can slow further degradation. Enable Low Power Mode in Settings > Battery to reduce processor speed and background activity, which cuts the strain on the battery. Keep the phone out of direct sunlight and away from heat sources. Avoid letting the battery drain completely, and avoid charging to 100 percent every single day if you can — charging to 80 percent and discharging to 20 percent is gentler on the cell.

If your phone is still under warranty or AppleCare+, do not attempt to replace the battery yourself. Opening the phone voids the warranty, and lithium-ion batteries can catch fire if punctured or bent. Even if the phone is out of warranty, a professional replacement is safer and often cheaper than the tools and parts you'd need to buy.

How long a new battery typically lasts

A replacement battery follows the same degradation curve as the original. You should expect it to reach 80 percent health again in roughly 18 to 36 months, depending on how you use and charge the phone. If you keep the phone in a cool environment, avoid fast-charging, and use Low Power Mode regularly, you may stretch that to four or five years before needing another replacement.

Most people replace their phone entirely before the battery needs a second replacement. But if you plan to keep your iPhone for five or more years, budgeting for a battery replacement every two to three years is realistic.

Frequently Asked Questions

Does Apple replace the battery for free if it's under warranty?

If your phone is within one year of purchase and the battery health has genuinely degraded, Apple replaces it at no cost. If you have AppleCare+, battery replacement is also free regardless of how old the phone is. Otherwise, you pay the standard service fee ($69–$99 depending on model).

What if my battery health is at 85 percent but my phone shuts down at 30 percent?

The health percentage and shutdown behavior can diverge because health measures total capacity, while shutdowns happen when the battery cannot deliver enough current under load. Bring the phone to Apple or a service provider; they can run diagnostics to confirm whether the battery is faulty and needs replacement regardless of the health number.

Can I replace the battery myself?

Lithium-ion batteries can catch fire if punctured or bent, and opening the phone voids any remaining warranty. Professional replacement is safer, faster, and often cheaper than buying the tools and parts yourself. If your phone is out of warranty, an independent shop is a lower-cost option than Apple.

Will replacing the battery fix my phone if it's running slowly?

Only if the slowness is caused by the battery. iPhones throttle processor speed when the battery cannot deliver enough current, which makes the phone feel sluggish. If slowness persists after battery replacement, the issue is likely the processor or storage, not the battery.

How do I know if my battery is defective versus just old?

If the phone shuts down unexpectedly, refuses to charge past a certain percentage, or shows a "Service Recommended" message in Settings, the battery is either defective or severely degraded and should be replaced. If the health is straightforward low but the phone behaves normally, you can wait until it reaches 80 percent or until the behavior becomes inconvenient.