Phone says 100% and dies the moment you unplug it: what to check first

If a phone shuts down the second the charger comes out, even with a full battery icon, the number is lying. It is lying in one specific way.

What “100%” actually means

Most phones estimate charge from battery voltage, not by counting electrons. A worn lithium cell can still sit at a normal resting voltage, so the phone reads 100%. The moment it is asked for real current (screen, radio, camera), the voltage sags and the phone decides the battery is empty and cuts off. With the charger attached, no current is needed from the cell, so everything looks fine.

That is why the symptom is “dies when unplugged,” not “dies after twenty minutes.” It is a load problem, not a charge problem.

Check these first (free, ten minutes)

1. Dies under load, or instantly? Unplug and leave it on the home screen. If it survives idle but dies when you open the camera or take a call, it is the cell.
2. Does it survive in airplane mode? Rules out a rogue app pulling current. Rarely the cause, free to test.
3. Watch the percentage for a minute after unplugging. If it collapses 100 to 20 to off, that is a fuel gauge reading a sagging cell.
4. Any swelling? Lay the phone face-down on a flat table and press a corner. If it rocks, stop. A swollen cell gets replaced, not kept on a charger.

What it probably is

The battery, meaning a cell that can no longer deliver current. Replacing it fixes this pattern most of the time. On iFixit's own thread for this exact symptom on an Infinix Smart 8, “replace the battery” is the accepted answer (jayeff, Sep 14 2026).

The honest caveat

Sometimes it is not the battery. A tired charging board, a worn connector, or a power-management fault can mimic it. So the order matters: battery first (cheapest, most likely), and if the symptom survives a known-good battery, then look at the board. Do not buy a board before the battery.

If a shop says “the motherboard is gone, it will be expensive” before anyone has tried a battery, ask them why. That is a fair question.

Want the map first

Send the make, model, and exactly when it dies. I will say what to check first and in what order. First look free, [email protected]