Battery life is great! I use rechargeable batteries and they last quite awhile.
My only complaint is the "low signal" message that kept coming up. I finally disabled the messages. I don't use the magnifier very often, but have heard that others had mixed results with that feature.
Click below to buy it at Amazon:
Microsoft Wireless Laser Mouse 5000 - Metallic Black (63A-00001)
Update: May 2014
My husband and I each have this mouse for our computers. We've had them for 3.5 years and they're still going strong! :)