Over the years, I've regularly been getting questions from people about wireless charging and whether the heat that is generated by the charger is damaging to the smartphone. But since the coronavirus COVID-19 pandemic, these questions have increased dramatically. I presume because more people are working from home and using their wireless chargers more.
I left the charger on overnight with nothing on it, and by the morning it was 19.3°C, while the surrounding area on the wooden table was 17.2°C.
Then I placed the iPhone 11 Pro Max in the case on the charger and let it charge for about 30 minutes and took the temperature again. Now the charger was up to just under 32°C, and the temperature of the table around it had increased by about a degree.
I came back about 30 minutes later, after the iPhone had been charging for about an hour and the charging pad was creeping up close to 35°C and the area immediately surrounding the pad was up to 23.5°C.
Nothing really to worry about.
I let the phone charge for another hour, so the phone had been charging for about two hours and had just hit 100 percent charge. The charging pad had already cooled down to below 30°C, with the surrounding temperature about 20°C.
I left the phone on the charger for another ten minutes or so, and it seemed that the temperatures had stabilized with the charger at a shade below 30°C, and the surrounding temperature about 20°C.
The bottom line is that these temperatures are nothing to worry about.
Sure, the handset and charge pad feel warm, but these are well inside the normal operating temperatures of modern smartphones.
If you want the charging to be cooler, remove any cases, don't charge the phone in direct blazing sunlight, and keep the pad on a hard surface (not on blankets or anything that might block the air holes).