Hmmm. Can't believe what you read nowadays anymore. I bought a Microsoft Wireless Mobile Mouse 4000 to replace an ailing optical laser mouse that's on its last legs, and on the package it said that one "AA" battery would last for one entire year without replacing. What it meant was, it would have took until the next spring before it's time to replace the battery.
Apparently, the mouse doesn't think like that, it appears, and when I was looking down at it, there was a red warning light indicating that the single battery had already been exhausted from use. Between surfing the web and playing some Team Fortress 2 now and then this is more than just a "mobile" mouse.