Battery, what battery? EDIT: Didn't see the previous post, no point saying the same thing Also, it might be the cable. This happened to my old USB Microsoft IntelliMouse.
Since you're playing games, like TF2, as aforementioned, you would be moving your mouse more, causing the cable to twist and contort. And the issue we should all know about cables are breakages. Could be a loose connection to the mice's circuit board, etc.
If it's past the warranty (2 years), then you can be adventurous and open up the mouse to check the joints.
But if it is still under warranty, then you should submit an RMA.