The batteries installed in my KX2 very quickly reached such a low voltage that the transmitting power was only 5W.
That’s why I only use them as a backup and always carry an external power supply that lasts me a whole day. With it, I can do several summits a day. It can also be charged in the car while driving to the next summit.
And yes - the built-in speaker is not exactly hifi. But in order not to disturb the tranquillity of the landscape (or other people), I’m using my headphones.
73 Armin