I have since some time the same problem in that the mouse pointer is not moving reliably i.e at full (expected) speed. Very annoying. Cleaning the laser lenses and replacing the batteries (to a B-brand admittedly) did not solve the issue. Battery status according to iMac = 100%. I then completely removed the plastic gliders and the mouse did work again as expected. Putting back the gliders brought back the problem. I suspect that due to either age (10y plus) or maybe a voltage level issue with the brand of batteries, the laser is no longer working at full power, reducing its capability to track the movement of the mouse on the surface.