When I used a wireless mouse, the battery lasted me ~3-4 months (I have a MX310 now, much better than the 500, and the 700 IMHO, i'll explain why).
310 - 36.99 CND, same technology as the -500 and -700, same general shape, just lacking two buttons, the
scroll buttons. Ooooo, I'm not going to use the scrool wheel, I'm going to use the BUTTONS! I'm lazy, so instead of rotating the wheel, I'll
press the button (which probably requires more enegry anyways)!
MX500 - 2 extra buttons for 69.99 CND?
MX700 - Wireless, but slower communicating, for 89.99? The fact that I will eventully have to buy batteries also puts me off.
If I wanted to use a wireless mouse, I'd build an entertainment system, but then I'd just use that Gyratron mouse the senses movements in the air

.