It's a foreign idea, but when it comes to worrying about the battery, just "don't". The first day, I watched the battery on the Watch and eventually I convinced myself to habitually not notice it anymore. I've never ran out of battery once and I don't expect to. And that's a full day of replying to people, making a phone call, and working out with almost 40% left when I put it on the charger this evening.
If you do 15 min of full, continuous use, it's very realistic to go down to 90%. The Watch's credo (I believe) is that it aims to accomplish a lot in a very little amount of time. In return, it uses the battery much quicker than a phone (since it is so small). Instead of having to open your phone to check a message and reply to one, the Watch simplifies the process so that this can be accomplished in mere seconds much more conveniently. So I think as you get into the groove of things and treat the Watch as more of a reference and quick solution tool much like a real watch, the battery no longer becomes an issue. Maybe that will change as time progresses, but you'll fall into the groove of things. I know I did.
So many time/watch puns.