We rented a GL06P and the battery life varied based on how much we used it on my iPhone 5 and 3 other devices periodically (primarily google maps and hyperdia). There were a few days I needed to use the extra battery while out and about (heavy usage) but the unit usually lasted all day if I remembered to turn it off when I wasn't using it. I rented the extra battery but if you have one for your iPhone I believe you can just use that. Great little gadget!