The Galaxy Z Flip4 has a 3700 mAh battery (slightly bigger than the previous generation). It supports 25W fast wired charging and 15W wireless charging.

I usually take about 1 hour 30 mins to charge the phone from 0 to 100%. It isn't fast compared to some of the Chinese branded phones.

The wireless charging is slow. If you were to charge the phone wirelessly from 0 to 100%, it would take you more than 4 hours to do that. (It took me about 5 hours on my test)

I didn't experience overheating issues in my charging tests.

The progress of the wired charging test:
5 mins = 9% 36.3°C
30 mins = 40% 37.5°C
60 mins = 72% 38.5°C
1 hr 29mins = 99% 34.1°C

The progress of the wireless charging test:
5 mins = 5% 34.9°C
1 hr = 27% 41.6°C
2 hrs = 50% 41. 4°C
3 hrs = 72% 40.8°C
4 hrs = 87% 38.4°C