Your iPhone works perfectly while the cable is in. Pull it out and the screen goes black within seconds, so you are now carrying a phone that only lives near a plug socket. I know how limiting that is, and how much it feels like the phone has simply ended.
It probably has not. This particular symptom has a name, and following the tests in order tells you what it is before you spend anything.
I will walk it the way a technician would. Apple publishes that order on a page written for repairers, and it is not one owners ever get sent to.
Test the battery first, not the port
There is a reason for that order, and it is not a guess. Apple keeps troubleshooting pages written for people who service iPhones, and one of them sorts power problems into groups.
Apple, on battery, charging and power issues, lists among the issues to act on: "iPhone turns off immediately after disconnecting it from a power adapter".
That line sits under battery issues. Not power issues, which is where "iPhone won't turn on" lives. Not charging issues either.
That placement is the first useful thing you get. It tells you which of the three parts to test first, and Apple's own triage puts the battery ahead of the port and ahead of the software.
Test one, two minutes, and it settles the port
Before anything else, find out whether the charging connector is even involved. It takes two minutes.
Apple: "Attaching a wireless charger turns on iPhone if it's off. You can attach a wireless charger to help confirm whether the iPhone turns on or not. This is helpful when the charging connector might be damaged."
Borrow any Qi or MagSafe pad. Plug it into a wall socket rather than a laptop. Put the phone on it and wait a minute.
If the phone stays alive on the pad and dies the moment you lift it off, that clears three things at once. The port, the cable and the adapter. Power is reaching the phone perfectly well.
Apple: "Disconnect the wired charge cable before you test wireless charging. When both are used simultaneously, charging defaults to the wired connection." Otherwise you will think you are testing the pad while the cable is quietly doing the work.
If it will not stay alive on the pad either, that is still useful. Whatever is happening is not about the connector.
Test two, one screen, and it is the one that answers this
Now read what the phone thinks of its own battery. One screen, and it usually answers this outright.
On iPhone 15 and later, Apple's route is Settings, then Battery, then Battery Health. Apple says you will see the maximum capacity, "if a battery replacement is recommended, the cycle count, when your battery was manufactured, and when it was first used".
On iPhone 11, 12, 13 or 14, the route is Settings, then Battery, then Battery Health & Charging.
Cycle count is the number to look at, and Apple publishes what to expect. Batteries in iPhone 14 and earlier "are designed to retain 80 percent of their original capacity at 500 complete charge cycles under ideal conditions". For iPhone 15 and later it is 1000 cycles.
If your phone is well past that, with a maximum capacity in the seventies or lower, your explanation is sitting right there on the screen.
Why an old battery kills the phone only when the cable comes out
Here comes the part that explains the whole thing. Apple documents the mechanism in full. It just never joins that mechanism to this symptom.
Apple, on battery and performance: "A battery with a high impedance might not be able to provide sufficient power to the system that needs it." And: "A battery's impedance can increase if a battery has a higher chemical age."
What happens next is deliberate. Apple: "When the operations can no longer be supported with the full capabilities of the power management system, the system will perform a shutdown to preserve these electronic components. While this shutdown is intentional from the device perspective, it might be unexpected by the user."
This next step is ours rather than Apple's, and I want to be straight about that. With the cable in, the adapter is carrying the load. Take the cable out and the battery has to carry it alone. A battery that cannot is exposed at exactly that moment and never before it.
Apple does add the conditions that make it worse. Apple: "You're more likely to experience unexpected shutdowns when your battery has a low state of charge, a higher chemical age, or when you're in colder temperatures." And in extreme cases, "shutdowns can occur more frequently, making the device unreliable or unusable".
That last phrase describes your phone. Oddly, that is reassuring. It means you are at a known end state rather than in a mystery.
Test three, if it is dying rather than shutting down
A different fault looks identical from the outside. One wait separates them.
Apple: "The iPhone may have entered a deep discharge state that requires 20 to 30 minutes of charging to turn on. The charging icon should be visible after two minutes of charging."
Plug it into a wall adapter. Leave it completely alone for half an hour, and watch the first two minutes for the charging icon. No icon in two minutes points somewhere other than the battery.
Apple is specific about how you set this one up: use "a compatible charge cable to connect the iPhone to a power adapter that's plugged into an electrical outlet", and do not use "a computer port or wireless charging".
Our page on an iPhone that will not turn on at all covers the longer version of that wait, which Apple stretches to a full hour in some cases.
Test four, the wiggle, which is the cheapest of all
Does it survive unplugging sometimes and not others? Then check the connection itself before blaming anything.
Apple: "Gently move the cable around at the connection to ensure that there is no intermittent connection. If the connection appears to be intermittent using a functioning charge cable, the iPhone charging connector may be faulty or damaged."
Then clean it, Apple's way. Apple: "Gently clean the connector using a small, non-metallic, soft-bristled brush." Twist the bristles to lift debris, and brush it away from the connector rather than into it.
Apple's warnings here are firm, and I would follow them exactly. Unplug everything and turn your phone off first. Nothing containing bleach or hydrogen peroxide. No moisture in the openings. No compressed air.
Our page on a USB-C port that has stopped working has the model-by-model detail if this test is the one that fails.
What this is not, and it saves you reading the wrong page
Three other faults get called the same thing, and none of them behaves like yours.
- A phone that will not turn on at all, cable or no cable. Different symptom, different Apple page, and the fix starts with a long charge.
- A phone that restarts on its own and comes back by itself. That is a reboot loop rather than a shutdown, and our page on an iPhone that keeps restarting sorts the kinds.
- A battery that just runs down fast. Draining over an afternoon is a different problem from dying in three seconds off the cable.
What does not work
- Resetting All Settings, or erasing and restoring. No setting on the phone can raise the current a worn cell will deliver.
- Turning off Optimized Battery Charging. It changes when the phone charges, not what the battery can supply.
- A new cable or a bigger adapter. They matter for a phone that will not charge. This phone charges perfectly.
- A battery case as a permanent answer. It works, in the sense that it hides the fault, and you are still carrying a phone that cannot stand alone.
- Waiting for an iOS update. Apple treats the shutdown as intentional protection, so there is nothing for an update to correct.
Status: iOS 26.6, checked 17 August 2026. Apple lists this symptom by name in its battery group, doc 101969, and explains the shutdown mechanism on doc 101575 without linking the two.
Why does my iPhone turn off as soon as I unplug it?
Most often because the battery can no longer supply the power the phone needs on its own. Apple documents that a chemically aged battery has higher impedance and may not provide sufficient power, and that the system then shuts down on purpose to protect the components. With the charger attached the load is carried for it, which is why the phone only fails at the moment you disconnect.
Does this mean I need a new battery?
Check Battery Health first, at Settings then Battery. A high cycle count against Apple's design figures, 500 cycles for iPhone 14 and earlier and 1000 for iPhone 15 and later, plus a low maximum capacity, points that way. A battery replacement is far cheaper than a phone and Apple lists it as a service option.
Could it be the charging port instead of the battery?
The wireless charger test answers that. If the phone runs happily on a wireless pad and dies the second you lift it off, the port is not involved, because power was reaching the phone without it. Use the pad on its own, since a connected cable takes priority over wireless charging.
The Short Version
- Apple lists this exact symptom under battery issues, not under charging or power issues.
- Test one: run the phone on a wireless pad with no cable attached. Surviving there clears the port.
- Test two: read Battery Health, at Settings then Battery, and compare the cycle count to Apple's figures.
- Apple's own explanation is impedance. An aged battery may not supply enough power, so the system shuts down on purpose.
- Joining that to the unplugging moment is our reasoning, not Apple's sentence.
- Test three: if no charging icon appears within two minutes on a wall adapter, look elsewhere.
- Test four: wiggle the cable at the connector, then clean it with a dry non-metallic brush and nothing else.
Where to Next
A phone tethered to a wall feels like a phone you have already lost, and the instinct is to start pricing up a replacement.
Give it twenty minutes of tests instead. A wireless pad, one settings screen and a wiggle will usually tell you it is a battery, and a battery is the cheapest part of an iPhone to put right.
If your Battery Health screen shows a healthy capacity and a low cycle count and the phone still dies the second you unplug it, tell me what those two numbers are in the comments and we will work out what is left.
Isaac Smith is the founder and editor of PC Glance, a website that covers computers, laptops, and technology. He is a tech enthusiast and a computer geek who loves to share his insights and help his readers make smart choices when buying tech gadgets or laptops. He is always curious and updated about the latest tech trends.