I got a Creative Zen recently, and it definitely does not last
for 25 hours.
You can NEVER reach the stated battery life. To understand why,
this is what manufacturers do to test the battery life of their MP3
players:
1) Put songs into a playlist.
2) Played repeatedly without shuffle.
3) If possible to off backlight, it's switched off.
4) No EQ.
5) No skipping of tracks, just dump it there and let it
play.
Reason why you can never achieve the stated battery life is
simple. You'll definitely use the backlight, and you'll probably be
skipping tracks or using shuffle function. All these consume more
power. And if EQ is switched on, even worse. 
