You unplug your iPhone at 7 AM, and by lunch, you are anxiously hunting for a charger. It is the single most common frustration for smartphone users, but it does not always mean you need to spend a thousand dollars on a new device. Often, a simple battery replacement can restore your phone to its original speed and endurance for a fraction of the cost of an upgrade.

Many users mistake hardware degradation for software bugs or "planned obsolescence." While iOS updates can tax older phones, the culprit is usually simple chemistry. Lithium-ion batteries are consumable components. They are not designed to last forever, and once they cross a specific threshold, your phone will begin to act erratically. Identifying the difference between a glitch and a dying battery is the key to saving money and sanity. Here are the nine definitive signs that your iPhone battery has reached the end of its road.

1. Maximum Capacity Drops Below 80 Percent

The most reliable metric for battery health is hidden right inside your Settings menu. Apple provides a specific percentage that represents the current capacity of your battery compared to when it was new. If you ignore every other sign on this list, do not ignore this one.

Lithium-ion batteries chemically age over time. As they cycle through charges, the active material inside them degrades and holds less energy. Apple officially states that a normal battery is designed to retain up to 80 percent of its original capacity at 500 complete charge cycles. Once that number dips below 80 percent, the user experience degrades significantly. You will notice shorter run times and potentially unexpected behavior.

Check this immediately by going to Settings, selecting Battery, and then tapping Battery Health & Charging. If the Maximum Capacity number is 79 percent or lower, no amount of software updates or "calibration" tricks will fix it. The physical cell is degraded. Scheduling a replacement service is the only way to get your all-day battery life back.

2. Unexpected Shutdowns at 20 or 30 Percent

Few things are more annoying than your phone dying while the battery icon still shows plenty of charge remaining. You might be taking a photo or opening a map app with 30 percent battery left, and suddenly the screen goes black and the spinning wheel appears.

This happens because an aged battery typically has higher internal impedance. Simply put, the battery cannot deliver power fast enough when the processor demands a spike in energy. Even if there is "capacity" left in the tank, the battery cannot push the voltage out quickly enough to satisfy the hardware. The phone protects its electronic components by cutting power instantly to prevent voltage irregularity.

If this happens even once, check your Battery Health settings for a note about "Peak Performance Capability." If your phone has experienced an unexpected shutdown, iOS will automatically apply performance management. This is a clear signal that the battery is no longer capable of supporting the device's peak power requirements and needs to be swapped out.

3. The Interface Feels Sluggish and Slow

Many people believe their old iPhone gets slow because Apple wants them to buy a new one. In reality, the phone slows down to prevent the random shutdowns mentioned in the previous point. This is a feature called performance management, or throttling.

When a battery is weak, iOS intentionally slows down the processor (CPU) to ensure it does not draw more power than the battery can handle. You will notice this as stuttering scrolling, apps taking longer to launch, lower frame rates in games, or the camera taking forever to snap a picture. It feels like the phone is struggling to think.

You can temporarily disable this feature in the Battery Health settings to regain speed, but you risk your phone crashing randomly. The permanent fix is not a new phone, but a new battery. Once the fresh battery is installed, iOS detects the stable power source and automatically restores the processor to full speed. Your "old and slow" phone will instantly feel snappy again.

4. The Phone Gets Hot During Basic Tasks

It is normal for a phone to get warm while playing high-end 3D games or charging. It is not normal for your iPhone to feel hot to the touch while you are simply texting, browsing a website, or checking email.

Heat is a byproduct of electrical resistance. As the battery chemicals degrade, the internal resistance increases. This means the battery has to work much harder to convert stored chemical energy into electrical energy for your phone components. That wasted energy is released as heat. This creates a vicious cycle, as heat further damages the battery chemistry.

If your device feels uncomfortably warm on the back specifically where the battery is located, and you are not doing anything intensive, the battery is failing. This is a safety concern as much as a performance one. Continuing to use a battery that generates excessive heat can damage other internal components like the display or logic board.

5. The Screen is Lifting or Separating

This is the most critical and dangerous sign on the list. If you notice that your screen glass is slightly raised, pushing out of the frame, or if the glass feels "spongy" when you press on it, you likely have a swollen battery.

When lithium-ion batteries fail catastrophically or are damaged, they can produce gas internally. This gas inflates the sealed battery packet like a balloon. Since there is no room inside the iPhone for this expansion, the swelling battery pushes upwards against the display assembly and can pop the screen out of the chassis.

Do not try to push the screen back down. Puncturing a swollen battery can cause a thermal runaway event, leading to a fire. If you see physical deformation of your device, stop charging it immediately. Turn it off and take it to a professional repair shop. This is not a candidate for software troubleshooting; it is a hardware emergency.

6. Battery Percentage Jumps Wildly

A healthy battery discharges linearly. It goes from 100 to 90 to 80 in a predictable curve. A failing battery often behaves erratically. You might look at your phone and see 40 percent, put it in your pocket for five minutes, and pull it out to find it at 12 percent.

This happens because the chemical breakdown inside the cell creates "dead zones" or voltage irregularities. The software on the logic board struggles to read the true charge level because the voltage is fluctuating unpredictably. While simple calibration (draining to zero and charging to 100) can sometimes fix software confusion, persistent jumping is a hardware failure.

If you watch the percentage drop by 10 or 20 points in a matter of minutes without heavy usage, the cells are likely damaged. This makes the phone unreliable, as you never truly know how much time you have left before the device dies.

7. You Are Only Able to Use the Phone While Charging

If your iPhone dies the moment you unplug it, or within a few minutes of being disconnected from power, the battery has reached total failure. It has completely lost its ability to hold a charge.

At this stage, the battery is acting as a pass-through conductor rather than a storage device. The phone is running directly off the current from the charger. While the phone technically works, it has lost its utility as a mobile device.

Many users try to limp along with portable power banks, keeping the phone constantly tethered. This is a temporary and cumbersome solution. Replacing the battery is significantly cheaper than buying a series of power banks and charging cables to keep your device on life support.

8. Wireless Charging Stops Working Consistently

This is a subtle sign that often goes unnoticed or is blamed on the charger. If your iPhone used to charge wirelessly without issue but now constantly disconnects or fails to register on the pad, the battery might be the cause.

This relates back to the swelling issue mentioned earlier. Even minor swelling, invisible to the naked eye, can push the back glass slightly away from the internal charging coils or misalign the internal components. Additionally, the excessive heat generated by a failing battery can trigger the wireless charger's safety thermal cutoff, stopping the charge to prevent overheating.

If you have tested multiple wireless chargers and the result is the same, and your charging port works fine, the internal geometry of the phone has likely changed due to battery expansion. This warrants an immediate inspection.

9. The "Service" Message in Settings

Apple has built-in diagnostics that constantly monitor the health of the power management system. If you see a message at the top of the Battery Settings menu that says "Service," "Unknown Part," or "Important Battery Message," the phone is explicitly telling you the hardware is faulty.

This message appears when the battery health has degraded significantly below safe operating standards or if the system detects a sensor failure within the battery connector. Unlike the 80 percent threshold, which is a suggestion, the Service message is a warning.

Ignoring this message usually leads to the other symptoms listed above appearing rapidly. When the operating system flags a hardware component for service, trust the diagnostic. It is time to book an appointment with a technician.

Is It Worth the Repair Cost?

Deciding to repair an old phone versus buying a new one comes down to economics. A battery replacement typically costs between 50 and 90 dollars depending on the model. If your iPhone meets your needs otherwise - the camera is good enough and the screen is not cracked - spending less than 100 dollars to get another two years of life out of the device is a smart financial move. However, if the phone has other broken components or stopped receiving iOS security updates, put that money toward a newer model instead.