I use my iPhone and the free Trailguru App to track rides up to 4 hours with a fully charged battery. To get extra battery life (since the App requires that the screen remain on) I dim the brightness setting as much as possible. I've never run out of battery on a ride, but I've also never ridden for more than 3.5 hours. I've been very happy with the way it has performed - time, distance, speed, average speed, calories burned - though I don't feel the total elevation can be relied upon.