In an ideal environment, the M545 mouse can operate up to 82 feet (25 meters) away from the receiver.
If you're not getting this distance, try these suggestions:
Make sure the battery is fully charged
Move devices that emit radio waves or could cause radio interference away from your work area
(ex. cell phones, radios, wireless routers, microwaves)
To determine if your environment is shortening your operating range, try using your device in a different environment to see if the distance improves. If it does, look for other possible sources of interference you can remove from your work area.