I would say the battery lasts at least 15 min, and probably longer, but I haven't timed it, and I don't like to fully charge or discharge it, as that shortens the life of lithium ion batteries.
The spool doesn't come with much line on it. When you reload it, you can fit more on it, but it's still a pretty small spool. You really have to learn to cut with just the tip, as it will last longer and cut better. Of course, trimming around walls, it will keep breaking off. It's easy to put out more string though; it has a button for that, that you hit while running the trimmer.