Yeah, about 3 months from the Lithium ones that come with the mouse. 2 months for Duracell and and about a month for 2500mAh rechargeables. Doesn't sound much compared with good usb mice, but Bluetooth devices can really suck the juice. In my opinion, if you want a Bluetooth for your mac, the Apple one is the best way to go. Longing lasting batteries, smoothest motion and no wake up from sleep delay. Ooh, and if you're short of batteries, the BT mighty mouse can run from just ONE battery. I love mine!