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.
the MX can do 30 days easy. the problem was that a lot of MX mice where shipped with crappy batteries, Logitechs supplier gave them batteries that had lower maH and in general sucked, so some people got the good batteries and some got the bad. the bad ones also charged bad, so for those with replaceable Lithoum batteries logitech would send replacements, for those with non replaceable batteries logitech just replaced the mouse, and for those with regular NiCd rechargeables they sent replacements, despite the problem with these often being user fault for charging wrong. Not doing the long first time charge, and "spot" charging them instead of waiting for the battery to get low before recharging and semi regularly let the batteries drain completely or nearly so.