Short answer: a screen that dims itself and charging that stalls at the same percentage after an update is usually not a fault — it is iPhone heat protection doing its job. iOS has a layered system: in the substantial heat range it limits processor performance, in the overheated range it goes further and lowers display brightness and pauses charging, with some features restricted in extreme cases. Apple has documented this heat-protection behaviour for iOS 27, and it has been reported in the press — the system is protecting itself, not failing. There is only one correct response: get the heat out.
Why heat protection behaves this way
Processors and batteries are both temperature-sensitive. In sustained heat, running at full speed does not just feel worse in your hand — it accelerates battery ageing, so iOS deliberately gives up some performance and some experience to buy temperature headroom:
- Performance first. Peak processor output is reduced, which you feel as dropped frames, lag and slower app launches.
- Then brightness. The display is one of the largest single sources of power draw and heat, so lowering brightness cuts heat generation noticeably.
- Then charging. Charging produces its own heat, and charging while already hot stacks the two — so the system would rather stop charging than keep climbing.
- Features last. In extreme cases, things like the camera flash or other high-load features are temporarily disabled.
All of this happens on the system side. There is nothing to configure, and there is no switch to turn heat protection off — it is the last line of defence by design. For how the tiers are defined and what each one does, see iPhone heat levels and throttling.
Why charging stops part-way
A common concrete case: the phone is plugged in, the battery sits at the same percentage — often around 80% — and does not move, sometimes with a message that charging will resume once the temperature drops. That is normally paused charging, not a broken cable, adapter or battery.
The test is simple: let it cool and look again. Take the case off, stop the heavy apps, move it out of a hot car or out from under a duvet into a shaded, ventilated spot, and wait for the temperature to fall. Charging generally resumes by itself. If what you are really interested in is the heat that charging generates, see Why does an iPhone get warm while charging?.
The right order of steps
- Remove the case and magnetic accessories. Cheapest and fastest step available — a thick case noticeably impedes heat loss.
- Stop high-load apps. Navigation, heavy games, long video recording and video calls all hold power draw high; pausing them gives the system thermal headroom.
- Move it somewhere cool and ventilated to shed heat naturally. Do not keep gaming while charging, and do not smother it under bedding or cushions.
- Let it recover on its own. Once the temperature falls, brightness and charging normally return to normal — no restart and no settings change required.
- If you want less heat and less drain, Low Power Mode under
Settings → Batteryreduces background activity and some visual effects, at the cost of performance (see What is Low Power Mode?).
When it is actually a problem
Keep "the system is protecting itself" separate from "something is wrong", so you neither over-worry nor ignore a real issue:
- brightness and charging still do not recover after the phone is in a cool place, or dimming recurs repeatedly at ordinary temperatures — that deserves a closer look;
- it is hot to the touch in a cool room, not charging and with no heavy game running, and protection triggers often; see Why does my iPhone get hot?;
- the dimming does not track temperature at all (permanently dim, or changed manually in Settings) — that points at a display or settings issue rather than heat protection;
- Battery Health is already below 80%, which amplifies both drain and lag in the heat; see What is Battery Health?.
One last thing, emphatically: do not use a fridge. Condensation inside the chassis is far more dangerous than the heat itself, and a sudden temperature swing is unkind to the battery. By the same logic, do not replace a phone over settling-period warmth after an update — take the case off, stop the heavy use, and give it a little time.