I read about the new ipod mini's and various news sources are mentioning how they expanded the battery life:

The battery life of the second-generation mini models has also been improved. The playback time on a single charge is now 18 hours, up from the eight hours of previous models.

By the way I just recently found this and for those who don't want to send the battery back to Apple to be replaced can try this
Replace your iPod's battery

I was skeptical of opening the case up oneself but now I'm sure it's pretty easy by looking at the video. I'll probably get this for my bday next month instead of what I was thinking of before.