In recent decades, the costs of energy in dairy farming increased mainly due to rising energy prices but also due to increased mechanisation and automatisation. Electric energy in dairy farming is essentially used for milking and milk cooling. However, the energy consumption of automatic milking systems (AMS) depend on many factors (e.g., machine generations, machine configurations and settings, and operative conditions). To evaluate the differences in performance and energy efficiency of AMS, the impact of different technologies within the attachment arm in practical conditions, a detailed quantification of energy consumption was carried out on two consecutive single box automatic milking systems (AMS) of a dairy farm in southern Bavaria (Germany). The AMS equipped with an electrical drive of the attachment arm was more efficient and showed a higher capacity regarding cows in the herd. The replacement of the pneumatic drive with electrical drives leads to higher energy consumptions of the milking robot but reduces the energy consumption of the air compressor. Hence, the energy efficiency of the electric attachment arm showed strong advantages in the energetic efficiency of the whole milking process. Advances of sustainability due to the increased performance are and should be investigated in further research.