IPhone 13 overheat while charging

The phone has over-temperature protection. If the internal temperature exceeds design limits the phone will shut down and display a message saying it needs to cool off. If that doesn’t happen then the phone hasn’t gotten warm enough to damage the phone or the battery. If you don’t want it to get as warm as it does don’t fast charge it, use one of your old 5 watt chargers. Physics rules! In particular, the 2nd law of thermodynamics.

omir16 wrote:

I got an IPhone 13 recently, together with the 1 meter long lightning USB-C cable and an Apple certified 20W adapter.

The device gets very hot, even when charging without the case. I am afraid this might damage the battery on the long term -it is to my understanding that temperatures above 35°C do permanent damage to the Li-ion battery.

Is this normal? How can I fix it? Also, is there any way in which I could check the phone's battery temperature?

There isn't necessarily a precise temperature where a battery is damaged and where it's not. It's a continuum where in general a lower temperature is better for overall longevity. But it's not just the temperature, but how long it's at an elevated temperature as well as the state of charge. Having a battery at temperatures less than the thermal warning temp but for hours and hours could be worse than hitting thermal shutdown for just a few minutes.

https://batteryuniversity.com/article/**-808-how-to-prolong-lithium-based-batteries

Lithium-ion suffers from stress when exposed to heat, so does keeping a cell at a high charge voltage. A battery dwelling above 30°C (86°F) is considered elevated temperature and for most Li-ion a voltage above 4.10V/cell is deemed as high voltage. Exposing the battery to high temperature and dwelling in a full state-of-charge for an extended time can be more stressful than cycling.

That being said, I've encounter thermal protection where I was instructed to cool it down several times. Usually stuff like putting it on a seat in my car where the sun was heating it up. It was usually ready for operation in less than 5 minutes where it cooled down enough. The battery has over 500 cycles and it's still reporting 92% battery health. So obviously just hitting that designated temperature by itself didn't seriously damage the battery.

omir16 wrote:

Hi thanks for your reply! I got the 20W adapter after a friend’s recommendation. Would it be better then for a daily basis to use the 5W one? -I understand that it’ll charge more slowly but that battery health will be preserved for longer?

There's nothing particularly wrong with that. However, I save mine for convenience on the road and usually use an Apple OEM power adapter that was meant for iPads or other ones that produce at least 10.5W. For some reason, 2.1A (10.5W) is pretty common. It's a small difference, and won't really affect it much except in the middle of the charge range. The charging current is always limited when it gets about 70-75% to protect the battery.

Excessive heat (even without shutdown warnings) can affect battery longevity even if it's isn't catastrophic battery failure. Not sure what the deal is with the OP though.