I actually downgraded to a Logitech G400 from a Performance MX. I really loved the Performance MX but it only got about 3 days on a battery charge. Yes, I can run it with the USB cable plugged in but that kinda defeated the purpose of the 'wireless' part. The 30 day battery claim isnt even close and the Logitech forums are packed full of unhappy Perf MX users like myself.
Seems odd the solution to poor battery performance was to buy a wired mouse instead of just plugging the mouse you had in at night, but what do I know.
I mean, expecting (or advertising) 30 days out of a "performance" mouse of any kind is a bit silly. A decent mouse should be able to go a few days though, even my G700 can do that at the highest polling rate.