ALTERNATOR PULLEY RENAULT MEGAN II 1.5 DCI.

The case that this weekend on the highway, I notice some small pounding and downside, the battery breakdown witness is lit, I leave the highway stop and absurd that the auxiliary service strap had been removed or alternator and compressor of the clinatizer. I observe that the alternator's roller has a game forward and behind. My question is it normal for the Tega Pulley for that game?
or if that movement is a clutch of the roller itself. They would thank you for many to give me an answer. Thank you very much to everyone.