On the rare case I actually unplug it (you can have it plugged in fulltime like a wired mouse), it lasts for quite awhile, I don't think I've ever had it actually die even after like 5+ hours, but I don't really time it.
A buddy was looking for a new mouse and I got him to get one, he loves it too.
I might actually get it, I like how it has the quick disconnect thing on it (as you said it can be used as a wired mouse)
my keyboard still is trucking along after all these years (G15) while my razer mouse is ... slowly dying, i've tried cleaning everything, and it just seems like the clicky thingy is dying or not working right.