Perhaps in time, the handset loses the notion of the autonomy of the battery (the battery indicator appears half). In this case, repeat the procedure described in the manual at the first use of the phone.
Beware also (personal experience), it may hang completely and requires to enter a specific code to reset completely. (Code does not provide that Gigaset ... They prefer to charge you troubleshoot your friend ... Use Google in this case ... Key Words: C610H factory reset)