A method of communicating between a mobile communication device including a power supply, and a base station. The mobile device has first and second alternative communication modes, the first communication mode having higher quality of service and higher power consumption than the second communication mode. The second communication mode is adopted in response to a characteristic of the mobile device power supply indicative of a reduced reserve of power in the power supply, and a state indication is transmitted from the mobile device to the base station. The base station can respond to the state indication from the mobile device by modifying a communication characteristic of the base station with the mobile device, whereby to tend to compensate for the mobile device switching between the first and second communication modes.