A year or two ago I bought a Logitech Cordless Mouseman Optical 4-Button USB mouse (M/N M-RM63) for my desktop computer. It has worked flawlessly all this time and I don't remember changing the batteries, ever.
In contrast, last year I purchased a more problematic Targus Wireless Mini Optical Mouse (PAWM-10) for my laptop. Within a month or so it failed and I had to mail it to Targus for a replacement. Then I found that the batteries drain VERY quickly, even when I switch the mouse off. If I forget to turn off the mouse a couple of times, the batteries will die within two weeks.
I'm amazed at the difference between the mice.