I bought my significant other a Nano and she just loves it. The Nano gives you 14 hours of use, which I think is very good being so small and light. The battery is just like most cell phones, meaning you use it during the day and charge it at night. I would suggest though you also get an AC charger ($5 - $30), for those days that your on the road and you need to charge it. Or you can plug it into any USB capable computer to charge
I also have the 20gig (Touch bottons), that just died a few months ago - held up quite well for 3.5 years.
I was offered an ipod 20Gbs a few years ago and am still very happy with it.
I am very keen to buy an ipod nano 4Gbs (decent capacity + light weight) as a present for my wife but some comments regarding the battery life are worrying me.
Has somebody suggestions of replacement, or is this battery life not that bad?