1.The M11 Pro uses two AK4497 chips that consume a lot of power to achieve high sound quality. It generates more heat than other chips when it works. Therefore, the M11 Pro will also emit heat when it is working normally. 2.The battery capacity of M11pro is 4370mA while M11 is 3800mA instead.
https://www.amazon.com/FiiO-M11-Android-Lossless-Bluetooth/dp/B07XPTM5YS

