Battery-powered mice are wireless and rely on the batteries to supply their power and keep them functioning. For this reason it is important for the user to be savvy with regards to noticing when they are running low, and replacing them. The batteries for Dell mice slot into the shell of the mouse so it is a relatively easy process to replace them.
Check that the LED red light on the underside of the mouse is on. If that light is off or faint then that is a sign your batteries need replacing.
Find the battery port on the underside of the mouse and remove the small plastic door which shields the batteries.
Remove the old batteries. Simply flick the batteries out with your fingers. The batteries in a dell mouse are not locked in so it will be easy.
Put the new batteries in the battery port of the mouse. Replace the door of the mouse, and flip the mouse back over. It should now be working perfectly.