Not terrible. A little over 16 hours of use ended up with 53% battery remaining. That was using it a lot since I was playing around with it. I'm used to charging my phone and my Pebble every night, so it wasn't a big deal. The charging system itself is annoying, though. The magnetic cable on the Pebble is a lot easier to use.
You charge your Pebble every night? I only charge mine once every 5 days or so.