Im liking the 525 logi wireless here and only had it 2 days. They claim a whopping 3 years on 2 aa batts. It a bit heavy but Id take a one aa batt with a year or so of life in a higher end wireless mouse. Im really surprised how good the lag is. I had tried some MS wireles mice and they were pretty bad with dropouts and lag. But that was some years ago.
Ill keep running this basic 525 and then spring for a bit more gamer Logitech model in a few weeks.
Really impressed what logitech has done here even with their low end mice.