The number of applications using machine-2-machine-(M2M)-communication is rapidly increasing. Whereas, development and installation of systems using standard mobile communication systems is a mere development task, the implementation of battery-powered sensors systems comes with severe challenges, especially, if long operation times in the range of years should be achieved. For these systems, optimization not only from hardware, but also from firmware side is required. The contribution gives an overview on the GPRS and the UMTS protocol elements being critical to energy consumption and shows results of power and energy consumptions measurements under various conditions. Therefore, it will also give an insight into the respective measurement systems. Finally, recommendations for optimization with regard to energy-consumption are given.