I would personally hate to see less than 4 hours battery life, 5 or better would be ideal. That will get one cross country on a direct flight, or to Hawaii from the west coast. 5 hours falls way short if one is flying to europe or Asia. 4 to 5 hours would more than cover the hour or two I get in the living room before every one else wakes up. The rest of the time, I'll plug into a wall outlet. Any less than 4 hours and a plug in digital dock and a desk top amp start to look pretty good for a similar price.