Your iPhone will slow down and shut off unexpectedly

When an iPhone battery degrades past a certain point, Apple's software deliberately reduces your phone's performance to prevent sudden shutdowns. This slowdown happens automatically — you do not control it, and you cannot turn it off. Your apps will take longer to open, web pages will load slower, and games will stutter. The phone is protecting itself from the power demands that would cause it to die mid-use.

Eventually, the battery will not hold enough charge to power the phone at all, even at reduced speed. You may see the low-battery warning at 20 percent, then at 10 percent, then the phone shuts down completely — even though the battery indicator shows charge remaining. This happens because the battery cannot deliver the current your iPhone needs in that moment, so the system cuts power rather than risk damage to internal components.

Key Takeaways

  • iPhones with degraded batteries run slower automatically, a feature Apple added to prevent unexpected shutdowns.
  • Your phone will eventually shut down during normal use, even when the battery shows remaining charge.
  • A failing battery can damage other hardware over time, particularly the logic board and charging port.
  • Battery replacement costs between $50 and $100 depending on your iPhone model and where you go.
  • Waiting to replace a battery costs more in the long run because hardware damage becomes expensive to repair.

Physical damage spreads to other components

A degraded battery swells as it ages. This swelling pushes against the screen, the logic board, and the charging port. Over weeks or months, this pressure can crack the screen from the inside, warp the frame, or damage the charging connector so your phone no longer charges reliably. Once the charging port is damaged, you are looking at a $200 to $400 repair instead of a $70 battery replacement.

The battery can also leak electrolyte, a corrosive chemical inside the cell. If this leaks onto the logic board — the main circuit board that runs your phone — it corrodes the connections and can cause permanent hardware failure. At that point, your phone may not power on at all, and repair becomes much more expensive or impossible.

Your phone becomes unreliable for emergencies

A phone that shuts down without warning is not a phone you can depend on. If you are driving and your GPS dies, if you need to call for help and your phone powers off, or if you are away from home and cannot reach anyone, a failing battery puts you in a real situation. The slowdown also makes your phone unsafe to use while driving or in situations where you need quick access to emergency contacts or maps.

Battery degradation is gradual, so you may not notice how bad it has become until you are in a moment where you need your phone to work. By then, it is too late to plan a replacement.

Replacement costs less than damage repair

Apple charges $69 for battery replacement on most iPhone models, though some older or larger models cost up to $99. Third-party repair shops often charge $40 to $60. Compare that to the cost of repairing a cracked screen ($200 to $400), a damaged charging port ($150 to $300), or a logic board failure ($300 to $600). A battery replacement now prevents all of those repairs later.

If your phone is still under AppleCare+, battery replacement is covered at no cost as long as the battery capacity has dropped below 80 percent. Check your coverage in the Settings app under Battery Health & Charging to see if you have AppleCare+ and whether your battery qualifies.

Your phone may not receive software updates

Apple sometimes prevents phones with severely degraded batteries from installing major iOS updates. The system needs enough power to complete the update process without shutting down mid-installation, which can corrupt your phone. If your battery is too weak, you will be stuck on an older version of iOS, which means you miss security patches and new features.

This is a safety measure, but it also means your phone becomes less find over time. Older iOS versions have known security vulnerabilities that newer versions fix. The longer you wait to replace the battery, the longer your phone stays exposed to those risks.

Resale value drops significantly

If you ever want to sell or trade in your iPhone, a phone with a degraded battery is worth much less. Trade-in programs check battery health as part of their evaluation. A phone with 80 percent battery capacity might be worth $200, while the same phone with 50 percent capacity might be worth $100 or less. That $70 battery replacement could have protected $100 in resale value.

Even if you plan to keep your phone for years, battery replacement is an investment in keeping that device usable and valuable. It is one of the cheapest maintenance tasks you can do.

How to know if your battery needs replacement

Open Settings, tap Battery, then Battery Health & Charging. Look at the "Battery Health" percentage. If it shows below 80 percent, your battery is degraded. If it shows below 50 percent, replacement is urgent — your phone will likely shut down unexpectedly and hardware damage is becoming more likely.

You can also watch for signs: your phone shuts down at 20 or 30 percent charge, it takes much longer to charge, or apps close unexpectedly when you switch between them. Any of these means your battery is failing and replacement should be your next step.

Frequently Asked Questions

Can I just use my iPhone with a bad battery?

You can, but it will be slow, unreliable, and you risk damaging other parts of your phone. The longer you wait, the more expensive repairs become. A battery replacement now costs $50 to $100. Fixing a cracked screen or charging port costs $150 to $400.

Will my phone stop working completely if I don't replace the battery?

Eventually, yes. The battery will degrade to the point where it cannot power your phone at all, even for a few minutes. Before that happens, the phone will shut down randomly during normal use, making it unreliable for calls, navigation, or emergencies.

Is it cheaper to buy a new phone than replace the battery?

No. A new iPhone costs $800 to $1,500. A battery replacement costs $50 to $100. Unless your phone is already broken in other ways, battery replacement is far cheaper and keeps your current device working for years longer.

Can I replace the battery myself?

You can buy a replacement battery online for $20 to $40, but opening an iPhone requires special tools and risks damaging the screen, water seals, or internal components. Apple or a certified repair shop does it safely and includes a warranty on the work. The labor cost is worth the protection.

What if my phone is out of warranty?

Apple still replaces batteries outside of warranty at the standard price ($69 to $99 depending on model). You do not need AppleCare+ or an active warranty. Third-party repair shops often charge less and can usually do the work the same day.