When I was using my iPhone 3hrs was about it. I'd turn off Wifi and Bluetooth but leave the screen on at low illumination as I wanted to see the route, speed, etc.. With an aux battery and bluetooth sensors it would probably be fine. It's only recently that Bluetooth "Smart" has been introduced and there are sensors using it. BT Smart is much less power hungry/wasteful than original BT and makes BT sensors practical. Check to make sure you're phone supports BT Smart...