Introduzione

Use this guide to diagnose and repair an iPhone that won't start on battery power, but shows the Apple logo in a loop when connected to a charger. This symptom can happen when the battery is deeply discharged, damaged, unable to supply current, or unable to communicate with the logic board. The current-draw diagnosis can apply to the iPhone 4, 4S, 5, 5C, 5S, and newer iPhone models, but the disassembly shown here is written for an iPhone 4S. Other iPhone models may open differently and use different screws.

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Passo 1 Confirm the bootloop symptom

Press the power button with the iPhone unplugged and check whether the screen stays dark.
A battery-related case may show no empty-battery icon and no reaction on battery power.
Connect the iPhone to a charging cable or charging station with a current display.
Watch for an Apple logo that appears, disappears, and repeats without the phone starting.
A charging station may supply about 5.1 V while the current draw sits around 0.1 to 0.3 A and drops to 0 A when the logo goes dark.
A normal iPhone charging current is usually about 0.7 to 1 A.
The battery may be too discharged, damaged, unable to deliver current, or unable to communicate with the logic board.
Bootloops can also come from logic board faults, so this battery replacement is only one likely fix.

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Passo 2 Prepare safely

Unplug the iPhone and wait for the screen to go dark before opening it.
If the battery is swollen, hot, punctured, or smells sweet, stop and handle it as a fire hazard.
Don't bend, puncture, crush, or overheat a lithium-ion battery.
Use non-metal tools around the battery connector whenever possible to avoid shorts.
Keep the screws, rear case, and small battery contact organized for reassembly.

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Passo 3 Remove the rear case

Use a pentalobe screwdriver or T5 Torx screwdriver to remove the two bottom screws.
Press the rear case and slide it toward the top edge by a few millimeters.
Lift the rear case away from the iPhone.
Don't force the rear case because the small clips can break.
This opening method applies to the iPhone 4S used for this guide; other iPhone models may open differently.

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Passo 4 Disconnect the battery

Use a Phillips screwdriver to remove the two screws near the battery connector.
Lift the battery connector from its socket with a fingernail, nylon tool, or plastic tool.
Don't use a metal tool to lift the battery connector.
Use tweezers to remove the small contact near the battery connector.
Keep the small contact safe because it helps cellular reception.

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Passo 5 Remove the battery

Pull the battery removal tab if it is still attached and strong enough to lift the battery.
If the tab is missing or broken, slide a long flat plastic tool under the battery from the outer edge.
Lever the battery up slowly until the old adhesive releases.
Don't pry from the logic board side because the tool can press on and damage the logic board.
Don't puncture or sharply bend the battery while loosening the adhesive.

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Passo 6 Prepare the adhesive

Remove the old battery adhesive and any broken pull tab pieces from the battery well.
Apply fresh double-sided adhesive where the new battery will sit.
For an iPhone 4 or 4S, use double-sided adhesive if model-specific battery adhesive strips aren't available.
Precut battery adhesive strips are ideal when they fit the model.
Cut oversized adhesive to fit the battery area.
Use tweezers to peel one liner from the adhesive.

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Passo 7 Apply the adhesive

Place the exposed side of the adhesive in the battery well.
Press the adhesive down lightly so it bonds to the case.
Don't press hard because the display is on the other side of the case.
Warm the adhesive very lightly with a heat source if it needs help sticking.
Don't overheat the case because the backlight is directly behind this area.
Peel off the remaining adhesive liner while the adhesive is slightly warm.

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Passo 8 Install the new battery

Connect the new battery before seating it if its flex cable isn't pre-folded.
Use the connected flex cable to guide the battery into position without straining it.
Don't pinch or scrape nearby flex cables while lowering the battery.
Press the battery onto the double-sided adhesive so it stays in place.

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Passo 9 Secure the battery connector

Lift the battery connector enough to place the small contact back in position.
Use tweezers to install the small contact near the battery connector.
Press the battery connector back onto its socket.
Align the screw holes in the connector area.
Use a Phillips screwdriver to reinstall the two screws near the battery connector.
Make sure the small contact stays in place while you tighten the screws.

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Passo 10 Reinstall the rear case

Set the rear case a few millimeters above its fully closed position.
Slide the rear case downward until it seats.
Don't force the rear case; check for a trapped screw, leftover part, or missing part if it resists.
Use a pentalobe screwdriver or T5 Torx screwdriver to reinstall the two bottom screws.
Tighten the bottom screws until they are seated.

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Passo 11 Test charging and startup

Connect the iPhone to the charging cable or charging station.
A 0 A reading is normal before the charging cable is connected.
A very low reading, such as 0.05 A, can appear while the phone starts using battery power.
Wait for the iPhone to boot.
Watch for the charging current to rise into the normal range.
A stable reading around 0.9 A indicates normal charging.
The iPhone may vibrate when it starts.
Confirm the battery percentage rises after a short charge.

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Passo 12 Check the removed battery

Treat a running phone that charges around 0.45 A as suspect because it may charge about half as fast as normal.
Use a battery charging station to test or recharge the removed battery if you have one.
Disconnect the iPhone; the charging station should return to 0 A with nothing connected.
Connect the removed battery to the iPhone 4S port on the battery charging station.
Watch whether the current stabilizes, because a bad contact may cause unstable readings.
A removed battery that accepts 1.7 to nearly 2 A can still have been too discharged for the phone to detect.
The battery circuit may also fail to communicate with the logic board.
Test the removed battery in another phone if you need confirmation and can do so safely.

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Passo 13 Choose a reliable battery

Use a replacement battery that is known to work with the exact iPhone model.
Compatible batteries may use generic lithium cells with either a compatible generic circuit or a refurbished original charge circuit.
Batteries with refurbished original charge circuits and new lithium cells are usually the most compatible type.
Generic batteries may start the phone but fail to charge correctly or communicate with the logic board.
If the bootloop remains and current still drops to 0 A, troubleshoot logic board faults.
Battery replacement is an easy test for this bootloop pattern, but it isn't the only possible fix.

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Conclusione

If the iPhone boots and charging current stays near the normal range, let the new battery charge before regular use. Recycle the old battery through a battery recycler. Repair didn't go as planned? Try some basic troubleshooting, or ask our Answers community for help.

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