Phone getting hot while charging: what's normal and when to worry
You pick up the phone from the charger and the back is properly warm. Or it shows a message that charging is on hold. Charging always makes some heat; the question is how much, and whether something is adding to it.
Why charging makes heat
No charger is perfectly efficient. Energy is lost converting mains power to USB voltage, in the cable, in the phone's charging circuit converting it down again, and inside the battery itself, whose internal resistance turns a little of every charge into heat. The faster the charge, the more current flows, and the heat from resistance grows faster than the current does. That's why phones charge fastest when nearly empty and then slow down as they fill: they're managing heat and battery wear.
Wirebook's interactive lesson on heat lets you heat up a pretend phone and see why covers trap the warmth.
Everyday causes you can fix
| Cause | Why it adds heat | Fix |
|---|---|---|
| Using it while charging | Games, navigation, video calls and hotspot make the processor and radio hot on top of the charging heat | Let it charge in peace, or use a slower charger while you play |
| Wireless charging | Less efficient than a cable, and a misaligned coil wastes much more | Centre it on the pad, remove thick or metal-backed cases, use a cable when it's hot |
| Thick case, pillow or duvet | The heat can't escape | Charge on a hard surface in open air, case off if it's warm |
| Sun, car dashboard, windowsill | The phone starts hot before charging adds more | Shade, then charge once it has cooled |
| Busy after an update or new phone setup | Photos syncing, apps installing and indexing run hard, often while plugged in | Normal for a day or two; leave it on Wi-Fi to finish |
| Weak mobile signal | The radio transmits at high power | Wi-Fi calling or aeroplane mode while charging if you don't need signal |
What the phone does when it's too hot
Phones watch their battery temperature constantly. When it gets high they first slow charging, then pause it, and they may dim the screen and slow the processor (thermal throttling). An iPhone shows a message that charging is on hold until it returns to normal temperature; many Android phones show a similar “charging paused” or overheating notice. At extreme temperatures the phone may show a temperature warning and refuse to do anything until it cools. These are protections working, not faults.
Cool it down by unplugging it, taking the case off and putting it somewhere cool in the shade. Never in the fridge or freezer: sudden cold can make moisture condense inside.
Is heat bad for the battery?
Over months, yes. Lithium-ion batteries age fastest when they are both hot and full. That's why phones have optimised charging, which holds at 80% overnight and finishes just before you usually unplug, and why some let you cap charging at 80% permanently. Turning that on, and avoiding charging in heat, keeps the battery healthy for longer. Using a fast charger isn't harmful in itself: the phone decides how fast to charge and slows down as it warms.
Warning signs: unplug now
- The plug, cable end or charging port is hot, rather than the whole phone warm. That points to a damaged cable, debris in the port or a fault, and can scorch the connector.
- A burning or chemical smell, hissing, or smoke.
- The screen lifting, the back bulging, or the phone rocking on a table: signs of a swollen battery. Stop charging, don't press on it, and take it for repair.
- It's hot every time even on a slow charger with nothing running: get the battery checked.
Use the charger and cable from the phone maker or a reputable brand. Very cheap uncertified chargers can skip the protections that keep charging safe.
Charging in the cold is a different problem with its own risk: see is it bad to charge a phone in the cold?
Related
Moisture detected in the charging port · Phone hot when not charging · Why a hot phone slows down · Does fast charging damage the battery? · Power bank won't charge my phone (or is slow) · Laptop plugged in but not charging · Power bank mAh vs Wh · Is it bad to charge a phone in the cold? · Why phones drain fast in the car or on the train · USB-C cables explained: which one charges a laptop · Why phones stop at 80% overnight · Earbuds or case not charging · Interactive: why phones and computers get hot
Questions
Is it normal for my phone to get warm while charging?
Yes, some warmth is normal, especially with fast or wireless charging. If it's too hot to hold comfortably, unplug it, take the case off and let it cool.
Why does my iPhone say charging is on hold?
The battery is too warm (or too cold), so the phone pauses charging to protect it. It resumes by itself once the iPhone returns to normal temperature.
Does wireless charging make phones hotter?
Usually, yes. Wireless charging is less efficient than a cable, and more so if the phone isn't centred on the pad or the case is thick.
Can I put a hot phone in the fridge?
No. Sudden cold can cause condensation inside the phone. Unplug it, remove the case and leave it somewhere cool and shaded.
Is fast charging bad for my phone's battery?
Not on its own. The phone controls the speed and slows down as the battery fills or warms. Heat and being kept at 100% for long periods matter more.
Published · updated .