I might of found a fix for this problem everyone..charge your Zune fully and then do a hard reset on it (back button + up button) and let it reset. Then see how long your battery life is. Mine was doing this, but it's been two days and my battery has not done this. I seem to be getting even better battery life than I was before. I'm thinking that the Zune might not of reset itself when the new firmware went on it and so it needs to be reset fully. I would make sure to charge your zune all the way up though first..just to be sure it reads it correctly then.
Zune 120gb Red, 30gb White, 30gb Black|Zune Pass Subscriber