This is weird, my lumia doesn't get a terrible battery life with wp 8.1 preview., but neither an outstanding one. It lasts all day with a moderate use, but not sure with an hard use. I think I'll wait for the oficial Cyan release, and let's hope battery life would get improved. 😉
Btw, Nokia is running final testing and releasing the update. In Spain, lumia 625 and 925 are getting it!