I had the same problem & had a lot of helpful emails from Creative after which my battery life went from the same as yours to over 12 hours. This is what they said:
Do please try updating the firmware for your player.
After which try doing the following.
Unplug the Zen Micro player from the power outlet, let it play continually until there is no charge left in the battery. If the Zen Micro shuts off, turn it back on and try to play a few more songs again as it may turn off when
it detects a low battery charge. Turn off the player, and plug it to a power source to recharge the battery. Estimated amount of time to fully condition and recharge the battery is about 4-5 hours.
After doing the above, please rip a cd - mp3 files at 128 kbps and transfer them on Zen.
Do a full charge for your player again and just play those files. Please do remember to disable the Sleep Timer and Idle Shutdown functions for the player.Set the playmode to "Shuffle Repeat"
Smart Volume is turned off.
It worked a treat for me! If you need to know anything else, post back and I'll ferret around in the rest of the emails