FritzFon C5 read battery state

Is it possible to read the abttery state of a Fritzfon?
I will switch on and off the charger of the phone to save the battery life.

The battery status of the C5 is not even transmitted to the Fritzboy itself and the Fritzbox itself is the interface for TR064. The C5 unfortunately has no documented interface.

Here are the documentaries of AVM …