I just got one of these Thursday. Nice mouse. Battery had no charge when I opened it so I charged it for about 4-5 hours while I was away. Used it for several hours that night and all day Friday and Saturday. Now the battery indicator is down to 1 green light. I expect it to be red by the end of the next full day of use. That's less than 4 days with pretty moderate use (on and off the computer all day long, switching it off when I go to bed). Logitech claims up to 15 days... how can this be? I can always put it on the charger when I go to bed, but I feel like I'm getting gypped. How long does yours last and how must does it get used?