iPod Nano 4th Generation Battery
After 3 hours of hard work I did it !
It's the first time I try such a job, and I found it "quite easy" to change the battery with the guide. Just follow the pictures and you'll be done.
The hard work for me was the solder part - and a friend of mine gave me a hand as he was more used to do this.
You can do it, it worth a try :)