I do not think this is a duplicate of How to disable mouse power status in indicator-power?, which deals with the Unity panel rather than the xfce panel.
I recently purchased a new wireless mouse to replace my previous wired one. In my notification area, there is now a mouse icon.
I do not want this icon there, and besides, it appears to serve no useful purpose. Nothing appears when I hover over it or left-click on it. When I right-click on it, the battery monitor menu appears.
The application is not listed in the notification area settings, and changing the "when to show battery icon" settings had no effect.