There is a definite disparity in the quality of wireless mouses out there. I forget the cheap one I was using previously, but it would mess up all the time and I was constantly replacing batteries.
Funny thing, I was about to say I had switched back to a wired mouse and it's worked flawlessly for months, but I just looked and realized I'd gone with another wireless. This is a Logitech M310 and, as I said, it's been fantastic. I don't remember the last time I changed batteries in it. In fact, I haven't. It's still got the battery that came with it.