Benq wireless mouse

Got this a couple months ago (with wireless keyboard).
Normally put the computer to sleep if ti's not working on anythign at nite, and turn the mouse upside down (becuase its really sensitive ot movement - had a lot of times i wake up and the tower is on).
Anyways, I have noticed that it does not put itself to sleep, and i cant find any information on the net saying that it should or shouldnt. (just killing batteries staying on all the time...)
Model: m306
anyone help?